You would only need 2 if your room ambient is very low since a UTH provides a basking area but doesn't do much for ambient temps in either a plastic tub or a glass tank. Zoo Med sells Repti Therm mats on Amazon, I would get 1 or 2 12x8's.
Whether or not you need ventilation holes depends on the substrate you use. If you're using cypress or coco-husk that hold a lot of water then you'll want some. If you're using paper or aspen then you likely can do without. While the lid is secure it's not airtight.