I play a 6pc drum kit and mic with a Beta 52 in the kick,(and plan to add a beta 91)SM 57 on snare(plan to add Beta 57)and AT PRO 25's on the 4 toms.
I play hard rock and would like to know what if anything I should gate and how to go about it!
well, it can vary, depending on the type of music you play. if you are doing traditional jazz/bee bop, than you may get away with no gates at all.
but, judging by your setup (4toms) it sounds like you are into a little more modern of an outfit. fusion, metal, rock, country - ? hate to box you into a specific genre.
the fact is, you could use a gate on everything, but like everthing in music, less is more, dont overdo it. you want a quick attack time on the gate, and (on the toms at least, usually your kick) you want to have a nice release time, probably around 70-120+msec, something to let your drums ring out their natural tone, without chopping them off.
reverb sweetens everything up - not a lot of reverb - but just a little "room" to give it ambience. the thing you dont want is the ride cymbal above the floor tom or the hi-hat above the snare to get that same reverb, that's when it starts to sound plastic and treble-y.
thats where the gate comes in. set the threshold so your toms and other drums come trough, but the cymbals dont. that's the magic trick, it's a balance between volumes, and you may never get it to work - *perfectly*, but, you do want the gate to keep out most of that stuff that takes peoples heads' off at the FOH when you arent playing a specific drum, and keeps the cymbals out of the tom and and snare mics.
It may make even more sense if you can afford it to go with a gate that is frequency dependent. For instance you may not want to kill the transient tails from your cymbals but avoid the boomy or snappy bleed from the snare drum. In this instance frequency dependent gates are invaluable and make more musical sense with more of the desired effect. Companies like BSS and Drawmer are a couple of the manufacturers that make these. Let me know if you want further info.