1. Can’t see why not you just have to decide how you’re going to regulate the pressure (assuming you’ll have the top fitted).
2. The CO2 is added as the beer is dispensed from the PB. This helps with the pour and also stops air (oxygen) from entering the PB and spoiling your beer.
3. Don’t know. PBs not good for highly carbonated beers like larger. I don’t brew lagers so my experience is zero on this one. Sorry.