On my Ludwigs the floor tom mounts are about 5" from the resonant edge of the shell. 4-6" would work given you have the standard 21" or so long legs.
Best method for drilling? Use use a brad point bit or a Unibit. I've even used a 1/4" spade bit with success. The main thing to remember is to "punch" a starter hole with a nail or a punch tool and to have something clamped behind it to prevent blowout. I clamp a 1x2 inside the drum shell. using a punch helps keep the bit from "walking" during the beginning of drilling the hole.
Or if you're ever in the Austin area come to Round Rock and I can drill them for you.