Hello and Welcome!
I recommend you update your profile with your location. Much of beekeeping is location-specific, and we probably won't remember your location when you post questions. Having it in your profile will help us provide answers that are focused for your area.
Regarding screened bottom boards (SBB): ventilation is a good thing and SBBs are a useful tool in combating mites. I leave my SBBs on all winter, and we go weeks at a time below freezing. No problem.
Are you connected with a beekeeping club? That's another great way to learn about bees, as well as finding mentors and nearby beeks you will help you out. http://www.californiastatebeekeepers.com/affiliatedclubs.htm