The best time to use it is after you're already discovered in BVR, otherwise it's a big "Kill Me" sign. Didn't know that about the locking gate on jamming targets though, I never even pressed lock until it was inside... haha
As far as the loadout goes, I usually take 2 R-60 and 2 R-3R. I thought about taking the double racks, but my R-3Rs fall off all the time from maneuvering anyway (INCREDIBLY annoying), so I doubt the chances of a double rack staying on the aircraft for me, plus I really never find myself in a dogfight at all, usually it's R-3R and goodnight. Most of the time I only launch one and see how it explodes, my reasoning is that if it does hit then he's either going to be dead or so injured he may as well be dead, leaving me with another shot if needed on someone else.