A. 1) There is a major airport there, so flying should not be a problem.
2) There are many hotels all around the city and it's environs, finding a room at a reasonable rate should not be a problem.
3) Since San Diego encourages conventions, many of the hotels have special packages. Many offering discounts on major attractions: Sea World, San Diego Zoo, etc.
4) There are so many things to do in San Diego. We live about two miles north and go down often to play. As I mentioned Sea World, San Diego Zoo, there are also miles of beaches, from La Jolla down to Imperial. Del Mar Race track, Old Town San Diego, the waterfront shopping and dining area (the name escapes me now), Coronado, etc., etc. My absolute favorite place to go is Balboa Park. It was the home of the Worlds Fair at the turn of the century and the architecture of the buildings are a Spanish, Moorish style. The buildings now house wonderful museums of all kinds. It is really a lovely place.
5) I'm not sure about the Romance friendly aspect of the city, since I do not live there. I'm sure I can dig up information if you would like.
6) There are many wonderful restaurants in Old Town, The Gaslight District, The Waterfront and on and on....
7) The weather is wonderful in late April/May very springlike. We often have a mini heat wave in April. Of course with the El Nino thing still effecting the weather everywhere, there are never any guarantees.
Here is a great Web Site for more information about things to do and see in San Diego: VIVA SAN DIEGO http://www.vivasd.com/
There is a great animated map, just click and it will take you to the place you are interested in. Click on the photos for additional information. Well, I put my two cents in and I would love it if the convention was held in San Diego.
B. The weather is great!