Hi Dina,
I believe there is still plenty of room for good restaurants in Montenegro, and obvisouly my preference would be for Tivat since I live there 
If you manage a good mix of good atmosphere, good quality food, and reasonnable prices, you can manage to stay open all year. A good example is Al Posto Giusto in Porto Montenegro which is open all year round, and is busy even in week days in the winter.
Deliveries can be a good idea as well, especially if it is not Pizza which is the usual type of delivery food here.
Good luck
Carine