The KBS is really thin, like water thin. You should still do 2-3 coats with it not thinned.
For the "ventilated area" make sure you have a volatile chemical proof fan, or you may have a boom. You need a mask too, the fumes are horrible. I do all my dipping outdoors and then bring the baits inside to my drying racks to cure after about 15-30 minutes, almost all of the stink is gone by then.. I just dont like having them outside any longer for fear of dust/debris landing on them.
You need to empty the entire can into a mason jar, you can buy really large ones at walmart cheap, then just transfer into a tall skinny one for dipping and refill as needed. Be sure to put the plastic wrap under the lid. You will absolutely destroy the KBS can when you open it, I swear they glue the lid down with D2T when packaging the KBS. It will take screw drivers, tin snips, pry bars...
I have had KBS in a jar for 2 months and no issues, no preservative gasses. But if you do the two mason jar strategy like I suggested, definitely pick up some sort of heavy gas oxygen blocker for the storage jar... your argon will work fine.
2" baits per quart... hundreds. I think I dip around 50 cranks out of my tall skinny pint jar before refilling, and that's just refilling because its too low to dip anymore not because its empty. I've never really counted before though.
For buying, you can sometimes find discount codes on the lure making websites and facebook groups for buying direct.