I plan on going with a 7, 8 and 10 wt. I'm going to have the 7 outfitted with a wire leader for barracuda, the 8 outfitted for permit/bonefish, and the 10 for tarpon. I've never been to Belize, but I've fished in Puerto Rico, Bahamas, and the Keys for bonefish/cuda/tarpon.
I'm headed down there in May and have been doing tons of research for my trip. From what I can tell, you can go through one of the expensive lodges that cater to flyfisherman (Turneffe Flats/Lodge: http://www.tflats.com/fishing.html
, El Pescador: http://www.elpescador.com/
, ETC.) or you can get a local guide that isn't affiliated with these lodges. The only drawback from the lodges is that they want you to stay in their nice expensive rooms AND flyfish and a week could cost you $3000+. The reason I'm staying at Caulker is because I want my $$$ to go further. From what I can tell you can get a local guide for around $200/day and they can can do a great job of putting you on fish. The only drawback about the local guides is that they don't have access to flyshops and most don't carry their own gear. So, you'll have to bring everything that you need with you to Belize. Although, I think that El Pescador does have a small flyshop on their premises on Ambregris Caye.
For flylines, I'd get a Rio or SA WF flyline. They also have one's specifically designed for bonefish. if you have an extra spool, I'd bring it and rig it with a sinking tip just in case you see some low lying fish and need to get a fly down to them. (Just read an article in Saltwater Flyfishing mag. and the author suggest this).
With that being said, check out the following sites for additional flyfishing info. for Belize. http://www.actionbelize.com/fly_fishing_equip.htm http://CayeCaulker.org/ubb/Forum1/HTML/000123.html http://www.cybercayecaulker.com/seagull_tours.htm
Everyone on this board and at the email links for fishing lodges, etc. seem to be really helpful in pointing folks in the right direction.
Tight lines to you.....