Bad english sorry.
The window of vulnerability depend on the island, not the claim. Example : Southern island on B3 is open to pvp between 12 and 20 h, north island 18h to 23h, ...
Help to not concentrate the pvp in the same area, help players know where is the pvp (the window is always the same) and simplify your actual claim proposition to complexe.
And for solo/small companies the only thing that can really helps is factions, help them find safe harbors for rest and trading. With your system the best way i think is forced alliance (example at level 8 you can choose an alliance, pirate, navy, settlers, etc ... after you can only leave it, not join one, and in sea you can "raise the black" and choose to be temporary a pirate).