how the base rate would work for Scotland?
Assuming CU (not going to happen) it would be the same as it is now. You’d have to have your whole economic policy approved by the BoE though.
Assuming Sterlingisation you would have to set up your own Central Bank and set up your own currency reserves. This will cost a lot of money and involve a large amount of reserves which you’ll need to borrow at a higher rate as you’ve not honored your share of the UK debt.
This cost of borrowing will affect interest rates, which will be at a premium to what it will be for rUK. Scotlands interest rates could be 1-2% higher than rUK (£50-100 a month on a typical mortgage)
Also with Sterlingisation you’ll need to try and peg your currency to the £. Read about the ERM and find out how much fun that might be.