WRT to tariffs how many overseas provinces will disappear when he connects his empire? Also while we're discussing ideas is switching them cheesy? Probably not cheesy enough to put Prawn off changing one or two throughout the game but maybe cheesy to do it multiple times.
None, the capital isn't on the continent so nothing more will be connected.
As far as changing NIs goes, no way that's cheesy IMO. A basic game mechanic that punishes you quite sufficiently compared to the small advantage it may bring. That said, I'm not sure any changes are needed.