As long as you have a good lawyer helping you out, setting up a company and getting residence that way in Montenegro is easy and quite cheap. Realistically, the whole process takes one to two months. IIRC, you are expected to sign a one-year lease to get your temporary residence valid for one year. You have to renew this four times. After five years, you can get permanent residence.
Banking is OK. Despite using EUR, Montenegro is not a SEPA member so you're relying on SWIFT wires for moving money in and out. Slower and more expensive. There is a decent range and selection of banks, including Erste and OTP (CKB) if you want banks of EU origin.
Taxes are low. You can get lower taxes elsewhere but if you factor in costs of living, Montenegro might still be the better deal.
Montenegro has been working towards EU membership but estimates of completion vary from three to five years, to practically never.