I think everything you cite can be done in day trips from San Pedro (with the possible exception of jungle tours), but you'll have long days with a lot of travelling and limited time doing whatever the target activity is. It'll also cost a great deal more than doing it from an appropriate base on the mainland. Personally, I would have my dive vacation first, and then go and stay in or near San Ignacio for the inland bit. Apart from anything else, the cost of living there is on all fronts much less than on Ambergris Caye. In two weeks you could do your diving and get to Tikal, though you'd have to sacrifice some of the other activities.You really want to stay at Tikal overnight if it is at all possible. From Tikal (actually Flores) you could fly directly to Belize City for your return home, though this is not as cheap as it is convenient.