Well, it will all depend on how many wires will need to go on the other side of the FW. In most cases, there is a need for two passes, one on each side towards the upper part of the FW somewhat close to the engine mount point to the FW. Just try to think ahead before you drill those holes. Will you be able to pull the battery out, will it interfere with mags/oil filter or be in the way of oil cooler, will the wires be suspended in the air for some distance before entering the FW, things in that nature.
Good luck