Those were unnecessary responses. Sorry for that. But TripAdvisor, does have more members; open minded and well traveled.
For the Bulgaria entry requirements you really have to check out their official web site. Any advice here from any poster is going to be questionable (as you may have already noted) and its just too important to get wrong.
Sunny Beach? It's been several years and with the Russian economy in the tank the last few years maybe things have changed, but my last visit it was largely a Russian tourist destination. Not that that was bad.
Can't help you on the hotel as I stayed in Nesebar and just crossed over to lay on the beach (very good). But do be sure to take a tour (or just walk around) Nesebar while you are there.
May? Its going to be a bit cool 55F to 70F. Beautiful part of the world. Enjoy, not a bad way to spend a few days in May.
Oh, never had a bad meal, but never had one that impressed me either. Beer is cheap. Nesebar is cheaper than Sunny Beach. I have plans to be in Odesa in June, Sunny Beach might make a good Plan B, thanks for making me think of it.