One thing you have to keep in mind is that a traditional seastead also doesn't put you out of reach of the 'evil empires'. Large goverments have few compunctions about invading smaller nations when it's to their benefit. The first seasteads will either have to be extremely militarily advanced while not instigating at all (think porcupine, and read The Transhumanist Wager for an example of one) or else have strong alliances (and therefore restrictions) with nearby nations.