Welcome to your new obsession,
I use exterior urethane, just let it cure for about a week before putting bees in. Mann Lake is a good company, but most of them are, only reason why there big lol. Some of the smaller companys may have better deals and its always a good idea to help the little guys instead of making the rich, richer.
And its not to soon for sure, you have lots of reading and studying to do, try and get involved with your local bee club. You will learn a lot here too, there are some of the best bee keepers in the country here. But for the time being, read read read