Yes, a mat on the back or side will work. Make sure it's big enough for the tank. You want to be aiming for around half of the enclosure to be at the upper reaches of its temperature requirements. With too small a mat you can end up with only a tiny area being warm enough, and the rest of the tank being too cold.
Lighting certainly isn't necessary but you can light the enclosure during the daytime if you choose.
Restricted ventilation will help to keep the humidity high. No ventilation will cause stagnant air and encourage mould etc. Are you able to get the glass top drilled?
Forest scorpions i.e. Pandinus spp. and Heterometrus spp., are generally trouble free and make good first scorpions.