I agree too tall! 12 to 18 inches max, higher is just complicating the whole thing for no reason. Well designed you should be able to manage with a UTH and perhaps a fluorescent light only.
see above.
however if you do decide to opt for the taller enclosure and need a heat panel, make sure it's connected to a thermostat. and look to RBI first. they have some of the best options for RHPs and excellent customer service.