1) we dont know and 2 we dont know
the only thing we know is that the whole thing will do Alex Salmond an awful lot of good ( he becomes a prime mininster ) and just about nothing else.
1 we should negotiate an undefended border - such as America/Canada or ROI/Northern Ireland. It would not surprise me if no one has yet thought of this.
2. voting is usually on residence. if you pay your taxes you get a vote. This will be a domestic thing for the Scots. The Irish in the UK have special voting rights in the UK. I have no idea if this will be carried over if Scotland becomes independent. It would not surprise me at all if no one has thought of this.