Try Orlando Hotels & Attractions on this board. There have been several beach discussions there. People have gotten good response from both the Gulf & Atlantic. Do a search, & ask your specific questions. Another source is
www.tripadvisor.com. They have a forum on their site. Once you decide which beach you want to visit, you can search the forum for that beach. The closest & most populated beach on the Gulf, is Clearwater beach. We haven't been over there, since the hurricanes, but I haven't heard of any significant damage. They have a huge white, sandy beach. The water is clearer than on the Atlantic, it is also calm, no waves. There's a county playground & pier with nightly entertainment. There's also dinner cruises & a pirate cruise for the entire family. If you're looking for an upscale resort, try the Don Cesar (a Loews hotel) on St. Petersburg beach. You can go snorkelling from there.
There's many beaches down through there. Where one ends, the other begins. The further down you go, the less populated it is. Clearwater is the 1st you will get to, coming from Tampa. Clearwater is close enough to Tampa, to take advantage of what the city has to offer. Busch Gardens is a pretty good drive, but worth it. You may want to look into leaving the beach a couple days early, and move to one of the area hotels. If you're into water parks, Adventure Island is next door to BG. There's too much to do in the Tampa/Clearwater/St. Pete area to even try to list it all. I'll stop with that, but if you have more specific questions, I'd be glad to try to answer them.
Edited to add: You will drive over Tampa Bay, between Tampa & Clearwater Beach. You still have a little way to go. Also, if you fly search both TPA (Tampa International) & PIE (St. Petersburg/Clearwater). TIA is on the west side of the city (close to the Bay), & PIE is actually in St. Pete.