What is the minimum seastead required to assert sovereignty?
I hereby declare that I have seasteaded Latitude 0 Longitude 0, and name it 0N0W (pronounced "Oh No!" - the "W" is silent!). I do not intend my seastead to have a permanent population but, then again, neither does the Vatican City. And I seriously doubt any of the new seasteads will have residents who don't leave on a regular basis. If Mitt Romney can declare his residence to be his child's unfinished basement, there really is no minimum residence standard anymore.
A PO Box suffices to establish residents for corporations in the Cormoros and so forth, so it should suffice for a seastead. I declare PO boxes at 0N0W are available (for a small fee perhaps ... get in early!)
Some may doubt the physical existence of such PO Boxes. I could challenge you to go there and disprove them, but the truth is this: the PO Boxes are virtual, accepting email only. There is no minimum size for a nation-state and therefore a nation state of size zero suffices. Nothing in the classical law of nations addresses email or the physical location of servers.
The first act of 0N0W will be to lay claim to everything within the customary zone of control (3 - 12 miles, I forget which), and economic control within the customer exclusive economic zone of about 200 miles. Leases are available!
I may have overlooked a few details, and would appreciate learning what I need to do to finish founding my very own nation-state. If Seattle parking rates go up I'd like to have diplomatic immunity.