You'll get differing answers about how much space is appropriate and whether tanks are any good. I'm of the opinion that assuming temperature and humidity requirements are met, more space is a good thing. The space additional space does mean you need more hides, vines, branches, etc - not just empty space. So personally I would say that if you go the tank route, get a 40 gal at least. This time of year it's also easy to find gigantic christmas tree storage bins, which I've heard recommended but haven't used.

Glass isn't as good at retaining heat as plastic is, and screen tops aren't good for humidity, BUT it is totally possible to heat and humidify a glass tank appropriately. If you insulate it well on three sides plus the bottom and cover the screen over, it's not going to be any worse at retaining heat and humidity than anything else. Insulating it is easy and cheap and you only have to do it once.

It varies from individual to individual, but plenty of males exceed three feet. If he's only recently gotten that big, I wouldn't necessarily assume he's done growing.