@Lordyaswas,
I, for one, think you are too much in extraordinarily hypothetical detail.
I believe Scotland will not secede from the UK, at least not this time.
But even it was the case, the separation would not automatically take place the following day.
Long months of political talks would ensue to define the answers to the technical questions you arose, along with many others.
Defining nationality would be one of the least easy.
You also ask questions of Scotland's future, within or out of the EU.
Were I British, I wouldn't care the least.
If they want independence, it's up to them to build their own future and up to you to do without them.