For beach, I think either CC or Hopkins + Tobacco. If you are concerned about decompression days, why not fly/drive/bus directly to Hopkins and chill for a few days, then move over to Tobacco.
Tobacco has great walk in snorkeling and easy access to dive sites where you won't see another boat, but the island itself gets a little stale after a while, thus Hopkins for beach and village life. Rather than tobacco, look at South Water Caye. IZE now accepts reservations from the public (rather than just research/educational groups) and they may be able to offer you an attractive package that includes dives. You can reverse the Hopkins-Caye order, depending on whether you want to dive or chill first.
After Tobacco (or SW) Caye, bus to San Ignacio, then over to Tikal for two nights. Tikal is not worth the trip unless you spend a minimum of one night, I would spend two and stay at the park, rather than Flores and have to take the shuttle back and forth. My preference for tour guides is to just go with one of the local guides at the entrance to the park, but you do need a guide for a half day anyway, the place is huge.
After Tikal you can fly directly into the Belize International airport from Flores or take the express bus to Belize City and taxi to the airport. It depends on your flight time, which one is better for you.