Sounds like Sevastopol will have the same status as the Kalingrad outpost which is part of Russia.
No - it would actually become a federal city - Moscow is a federal subject apart from the surrounding Moscow Oblast and St. Petersburg - also the other federal city in Russia - is a federal subject separate from the surrounding Leningrad Oblast.
SAevastopol would have a similar status in Russia.
Kaliningrad is the dung hole backwater of European Russia. All the neighboring countries of it have significantly better standards of living. Nobody lives there that has other options and those who can get an EU passport leave. I wouldn’t wish that future on anybody.