We do have a lot of different solutions to humidity issues. Try using plastic wrap to cover the screen except for a couple small areas in the corners. Try using a larger water bowl. You can also place the water bowl more over the under the tank heater. Don't forget about humid hides as well. (you may want to try searching for other solutions in case I forgot about something)

As for meal size, pinkie rats are only fed to young bps. Depending on the girth I would attempt to feed a prey item that is slightly smaller than the widest girth of your snake. I can only guess that at a little over 2' that would be close to a rat pup. You're going to have to to make a judgement call on that one.