I can help you with the Lamanai bit. At that time of year, since it will be in the dry season, you have multiple choices. I went there in February, and we got a rental 4x4 to drive up from Belize City. You take the main highway ( I think it is Highway 1) to Orange Walk, then hang a left and go halfway back toward Belize City on this other road. It will take you through the Mennonite farming communities. You can also get a float plane to take you to Lamanai, or you can take the really slow route and go by boat. Lamanai is wonderful - there are tons of opportunities for photographing temples and other archaeological relics, some really fantastic trees in the jungle, and all kinds of birds, flowers, and even Howler monkeys. It will be worth the effort (and it will be a considerable effort, with some risk) to get your 4x5 to the top of one of the temples that has been excavated at Lamanai - the platform at the very top is extremely small, but gives you a panoramic treetop view of the surrounding jungle. Also worth looking for at Lamanai is the ruins of the old british sugar mill. A strangler fig has grown out of the top and through the big iron gear wheels, and one of the beams has the name of a New Orleans foundry cast into it.
If you are going for primarily landscape, you might be better off with the Medium format rangefinder. It will be easier to carry around if you are going to climb any of the temples.