This is certainly a very promising idea, and I am quite sure that you'd be able to negotiate with a number of countries for favorable terms provided you offer them the prospect of stable GDP growth in some way.  Not necessarily taxation, but some economic tie-in to their economy, maybe by using local vendors for supplies or transport.  Countries are eager to do deals and joint ventures, and while this is a pretty extreme example of such an arrangement, I have no doubt you could get countries bidding for your business, similar to how Amazon recently set up a competition between cities to offer them the most favorable terms for their second headquarters.  There are many countries with coastlines around the world and if done properly you could essentially be granted "territory" status of the country, similar to how Guam, American Samoa, and Puerto Rico are for the United States.

As society moves forward, decentralizing everything, starting first with money as Bitcoin has made possible, but all legacy structures of power and control is very viable with technologies such as blockchain distributed ledger.  I'm going to look at the Seasteading Institute website closer and their spin-off Blue Frontiers.  This project in French Polynesia merits further review.

It's a great idea and please do keep posting your progress!