Anyone know?  Stop leak has successfully sealed the system and one can is moderately cooling the cabin, but I'm wondering if I need to add another one or two for optimal cooling.

Be careful with this.  It's best to look on your AC compressor.  There should be a label there that says how much oil and refrigerant is needed.  You do have proper guages don't you?  Do not guesstimate when it comes to adding refrigerant.  Use the guages, they'll tell you when it's charged properly.  MJD

It's probably 2-3 cans (30 +- 6 oz), but there may be no way of knowing how much is actually in the system.  The best way to tell is to get a manual.  It will tell how cold the air should be blowing from the vent compared to the outside temp.  If it's in spec, you're done.  If not, check the high & low side pressures with an A/C manifold (cheap at harborfreight, not bad at AutoZone).  If the pressures are low, add "a little" more (say, 1/4 can) and measure again; repeat until cooling is in spec.

Just get a can with a guage on it. About 20 bucks at china mart.