so now i have firm plans and will head inland to check out mayan ruins, caves, etc first
***I suggest going to San Ignacio (by bus from Belize City. There are several cheap places to stay there and it's a good jumping off point for ruins etc. You can comfortably go to Xunantunich and Cahal Pech in one day, but to go to Tikal is a considerable expedition - pretty costly - and you really need to allocate three days just to it. I'd skip it this time around. One set of ruins you can visit in a day trip is Caracol, and from what I hear (I haven't been there) it's well worth while. Another expedition to make from San Ignacio is a visit to the wet cave at Actun Tunichil Muknal ("ATM"). Read up about it - it's something many people come to Belize just to do.
and from there head to san pedro and hope to dive several days and include Hol Chan Marine reserve, blue hole day, Bacalar Chico Marine & Nature Reserve, M and M Caverns or Punta Azul Canyons, Half Moon Caye, the Aquarium, Silver Caves or Eagle Ray Wall, turneffe atoll wall dive called the Elbow or a wreck called the Sayonara. are these a good representation or should i hit others?
*** Don't be too prescriptive about the sites you want to visit, as shops may not go there that day. Of the local ones only Hol Chan and maybe Bacalar Chico will be choosable by you. Several of the sites you list are on outlying atolls and the trips there will be whold day affairs and quite pricey.
and can you recommend a dive shop that is safe but not expensive? i will bring my mask and snorkle, but will need to rent equipment
*** there are several good shops, mostly charging the same prices (because they all have the same costs - it's not a conspiracy). Some are cheaper, some more expensive, and I'd tend to disregard those. My personal favourite is Island Divers, but Chuck 'n Robbies, Reef Adventures, Amigos del Mar, Hugh Parkey's Belize Dive Connection all have good names and loyal followings.
. i have a flite out at 11.30am - do u think i can stay in san pedro the nite before and make a ferry out and over to BZ city and the airport in time to catch my flite?
*** Yes, you can - you can catch the 9am Tropic Air flight which will have you at the International Airport before 9:30. Personally I wouldn't trust Maya to that schedule - if I went with them I'd catch their 8am. The point is that they often give a considerable discount for cash, but their departure times can be pretty erratic. You can set your watch by Tropic. Don't even consider going by boat - it'll take too long and be too unpredictable.
There's a Mayan site on Ambergris Caye, but no ruins as such. The easiest ones to visit from San Pedro are at Lamanai, a boat trip and day's expedition.