Busch Gardens Tampa is a huge park. We spent four consecutive days there, but we like to see and do everything at a leisurely pace and we like to see things multiple times. Still, I would recommend at least two days there. SeaWorld is not quite as large, but I still couldn't see everything in a day. If you want to enjoy it all and take your time, I'd recommend two days there as well, however we spent three days at SeaWorld.
As far as a hotel near BGT, I loved staying at the Quality Inn at Ybor City/Florida Fairgrounds. Much of the area around BG is residential/commercial, not at all touristy, and it's not what you might consider the nicest of areas. In my experience, many of the budget chain motels near the park at not the best either. This particular Quality Inn is new, clean, relatively inexpensive, and around six miles from the park. The drive was easy took about 15 minutes.