There are a bunch of compromises involved with going to 8x10, and unless you are contact printing (which is a perfectly legitimate technique, mind!) I find 8x10 a hard sell. 4x5 negatives do sometimes come off as small, but only until you start working with them (enlarging, scanning, what have you). Are you prepared to deal with the weight costs, the rigidity requirements, the lenses, the $70 film holders, the cost for film, the depth of field issues?
I don't know what kind of camera you are making. If you're making a monorail, which is the way my Bender is designed, you can swap out the rear standard (and bellows) if you decide 4x5 is really too small later, and if you make the front standard big enough to handle the larger shutters. This is much lighter than 8x10 + reducing back.
If you really want to go with the bigger negative, then go for it, but know what you're getting into.