I think I can answer you first question and leave the rest for some one else to answer.
I used the small 12 OZ cans, DUEPOINT, and bought a AC filling kit from PepBoys for $7.oo. You might need to grind or cut the washer which comes with the kit, to make it fit on the can. But once you adjusted the size of washer, the T-Handle fits in pretty easy, and yes if you use half the can and leave the kit on the can, it will keep the freon from leaking.
I hope it helps.
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)