Looks nice, but I still maintain you should outsourse fabrication to a cabinetmaker. You could still do all the designs. As for knowing where the overflows are, it could be center, dual corner, corner....I would just drill it per customer asking. Also for plumbing, the person may want to have a closed loop or seaswirl or whatever. I think it would be better to let the customer do that him/herself, unless they ask for help which you could offer.