I agree the community part is the most potentially problematic.  However, I view it the same as self-defense: if some individual person is being immediately attacked, that individual should defend against the attack and the need for defense would be very obvious to the person being attacked.  If the collective community is being immediately attacked, then defend the community.  It's generally up to each person to decide what's appropriate, and I can see how that could be a source of disagreement in some cases.  In other cases, it could be extremely obvious when (collective) defense is needed.  It's in the most obvious cases where defense is most needed and appropriate.  If the need is less obvious, then maybe it's not really urgently needed.  That's where some discipline, planning and leadership could be useful. 

Does defensive leadership and planning lead to domination and tyranny?  That would be unlikely if the defensive force were made up of all adults.  Neither the Swiss militia nor the Swiss military officers have taken over the government of Switzerland in a military coup and imposed tyrannical rule.  They can't since essentially everyone is in the militia. 

If the Swiss military took over the Swiss government, they would essentially be taking over themselves.  They don't do that because they already *are* the government and the military.  It's about empowerment of individuals and the responsibility of individuals for that power.

An slightly-related older historical example is the Roman Republic.  The Republican age had a militia.  Therefore if the Republic wanted to have a foreign war, it needed to convince militia members to go.  Essentially there was no such thing as an unpopular major war since people would vote with their feet and not go to war.  When the Republic fell and became the Roman Empire, a professional standing army took the place of the militia.  There were lots of foreign wars and eventually the army was turned against the Roman people themselves.  That's where the expression "crossing the rubicon" comes from.  Julius Ceasar attacked the people with the army and the Empire eventually collapsed.   (Apologies to actual historians for the super condensed version, but I believe I got the general concepts correct.) 

As an aside, Wikipedia gives a pretty good description of the significance of crossing the Rubicon:

The river is notable as Roman law prohibited the Rubicon from being crossed by any Roman Army legion. The river was considered to mark the boundary between the Roman province of Cisalpine Gaul to the north and Italy proper to the south; the law thus protected the republic from internal military threat. When Julius Caesar crossed the Rubicon with his army in 49 BC, supposedly on January 10 of the Roman calendar, to make his way to Rome, he broke that law and made armed conflict inevitable. According to historian Suetonius, Caesar uttered the famous phrase ālea iacta est ("the die is cast").

 I cite the Roman Empire only as a historical example of the relative benefits of a popular militia over a standing army.  Non-initiation of force means defense only.

Agreed about signed contracts and everyone signing.  The beneficial community should have no freeloaders who did not sign.  Temporary vistors would be fine, of course, like a tourist versus a citizen.

Children would sign when they wanted to declare their adulthood, but if they refused to sign I don't see how they could be allowed to remain part of the community except as their parents' wards, i.e., they remain children under the protection and care of their parents.  Most children would prefer to become adults and would prepare for it by studying and learning the meaning of their adult responsibilities and preparing to accept them.  Rites of passage into adulthood happen in most cultures.

Disagree that the contract needs to be complex or spell out every possible situation.  It is as impossible to enumerate every scenario as it is possible to agree to the most basic ones.  Simpler is better.  If the contract is minimal and correct enough, then it should not need amendment.  Amendment may even be undesirable as a means towards a slippery slope of diminishing freedoms.

Regarding contract enfocement, that can be done by (competing) private arbitration companies.  In the U.S., private arbitration performs exactly that role.  Government courts and police are not necessary, nor necessarily desirable.

Regarding the role of police, if everyone is responsible for their own self-defense, then there would seem to be little need for police.  Remember that police are a relatively new invention that started out as court officers.  Recall that in England for many centuries before police existed there, ordinary people were expected to stop crimes personally and directly.  It was a civic duty for private individuals to stop crime.  The idea that police can protect people in general is largely erroneous.  There simply aren't enough police to stop crime effectively or practically.  They are not personal bodyguards.  Police are good at invesigating crimes after they have already occured.  It's much better if the crimes are deterred, stopped, or prevented from happening in the first place.  Only people defending themselves can accomplish that goal most of the time.  U.S. case law clearly shows that police have no duty to protect most individuals.  Naturally we could have private investigators in the rare event of actual crime.  However, if everyone defends himself or herself then there should be very little crime.  I've never heard of a robbery occurring at a gun range, police station or army patrol. Here's a quote from the article linked above:

Before the mid-1800s, American and British citizens - even in large cities - were expected to protect themselves and each other. Indeed, they were legally required to pursue and attempt to apprehend criminals. The notion of a police force in those days was abhorrent in England and America, where liberals viewed it as a form of the dreaded "standing army."

England's first police force, in London, was not instituted until 1827. The first such forces in America followed in New York, Boston, and Philadelphia during the period between 1835 and 1845. They were established only to augment citizen self-protection. It was never intended that they act affirmatively, prior to or during criminal activity or violence against individual citizens. Their duty was to protect society as a whole by deterrence; i.e., by systematically patrolling, detecting and apprehending criminals after the occurrence of crimes. There was no thought of police displacing the citizens' right of self-protection. Nor could they, even if it were intended.

Regarding respecting speech and thought, it's impossible to stop someone else's thoughts or speech except by initating force against them.  Choosing not to listen does not involve using force. It's also impossible to force someone to respect other ideas.  Ideas get their power from being convincing, meaningful and truthful.  Ideas are the opposite of force; they are how peaceful people interact.  Absent force, no one is required to listen.  Absent force, listening is done voluntarily or not at all. 

Here is an excellent piece about why self-defense creates peace and civilized behavior.

Regarding the extent of responsibility for defense, if the need is not obvious, then defense probably isn't needed.  (By analogy, would one use a fire extinguisher if there were no fire?  Probably not.)  That's an informal definition, but it probably should be made into a formal policy.  Collective defense is something that could perhaps be organized independently of an individual agreement for general membership.  On the other hand, it's useful to know up front how it is going to be accomplished, so there's something to be said for providing for it in an initial contract. 

If there is going to be a collective defense, then it should definitely be organized as a whole so that there are no internal factions potentially acting against each other.  Responsiblities and capabilities for collective defense should be kept simple and basic until they can become better organized and capable.  They should always be focussed on defense and not aggression.

Agreements with external nations/steads would be an entirely different matter, but could follow similar principles.  An external treaty for mutual trade, non-intervention and defense would probably be useful.  Nations should probably respect and interact with other nations in the same way that individuals should respect and interact with other individuals: peacefully, voluntarily, and for mutual benefit.

Natural law has varying interpretations itself, so yes, please elaborate.

As for my own position, i think it can be pretty accurately stated as follows: I dont feel an obligation to leave this world a better place than it would have been without me. I feel obliged not to make it any worse, but thats it. I hope to, and eventually even might make it a better place, but i categorically reject any attempts to try and force me to do so.

Thats pretty close to 'natural' law for most intents and purposes i suppose. But the moral absolutes and intentional is-ought obfuscation typical of many natural law 'aguments' are completely meaningless to me. I would not at all mind being neighbors with a natural law theorist, but i cannot imagine marrying one.

Not that i think its much of an argument, but for what its worth, i think this ethic will lead to an unprecedented maximization of utility. I dont feel any desire to discuss this in moral terms. As an emotivist, I dont care much for labels of good and evil. This is what i hope to achieve, period.

I think seasteading provides a real opportunity for cultivating this ethic together with likeminded people. This cultivating will probably involve a fair bit of telling eachother how good and awesome we are, and how much other people suck, but im confident that part will work itself out: what im more interested in are practical solutions and methods for keeping this system functioning and stable, such a dynamic geography, and taking active steps to prevent implicit social contracts from arising.