Generally speaking, a disc brake kit wouldn't affect the things you're talking about if you've still got the stock axle and aren't planning on some kind of giant exotic wheel. If you're looking into some kind of a front clip swap (Mustang II for example) that's when these factors come into play.
I put an ECI brake kit on my stock F-1. I'm running 15x6 Wheel Vintiques Gennie's on the front. I believe they are a 3.5" back space. 215/75/15 tires.
I recall a thread on the HAMB some years ago where a guy still had the stock 16x4.5" wheels and disc kit with no issues.