Scotland has about the same population as Norway or Ireland — 5.4 million — not Montenegro (0.62 million). GDP on the order of US $245Bn, 40-50 times higher than Montenegro. (And, geographically, 70% of the land area of England).

Politely, you might want to check your assumptions: I submit that if Norway can run a currency, or Ireland (which joined the Euro after running its own free-floating currency for multiple decades) then Scotland should be able to.