If firing a rimfire .22 in a basement, what do I need? What kind of bullet traps? Any recommended ammo (subsonic low velocity? CB? Non-lead?) or equipment?
Midway sells the Outers Rimfire Bullet Trap which is made for exactly what you are looking to do. Check them out at http://www.midwayusa.com . The stock number is 744-831 and cost is $61.99. This trap should handle any type of .22 rimfire ammo you would care to shoot at it.
The fan and open window is a must. But for a back stop, I use a cardboard box with old telephone books and other magazines set in the box on their ends. I sat the box on the shelf of a five foot step ladder. The reason I quit shooting in the basement was there is a lot of powder that is not burned and ends up making a mess on every thing. lottsa luck. Mike
Since my back will be to the garage door, it should be easy to vent... but in case ventilation isn't as easy as I think, are there additional measures? Surgical masks? Any specific types of ammo with very little lead smoke or no lead at all?
I strongly recommend against doing this. There is lead in the priming compound. Just opening a window and venting your basement will not be enough to prevent powder residue and lead from covering many surfaces in the basement. Your shoes will then track it throughout the rest of the house. Note that there will be enough unburnt powder in the residue to create something of a fire hazard as well.
If you want to shoot in the basement, get an air pistol. No lead. No powder residue. And quiet as well.