1. Big difference in M-Tech vs. M5 bumper is the M-Tech has brake ducts, the M5 has an alternator cooling duct (for the S38) and a blocked off duct on the other side of the bumper to make it appear matching.
2. Yes, both of them have the lower lip that you're speaking of. They're slightly different from each other and it's a bit hard to describe it. From a distance or to someone that doesn't know what to look for you'd probably not tell that there is any difference.
3. Should make no difference on installing either the M-Tech or M5 bumper.
4. Foglights are the same as I recall, should be no fitment issues.
5. Yes, no problems fitting the rear M5 bumper.
6. The M5 & M-Tech rear bumpers are identical. It's only the front bumpers that are different.
I should mention that my E34 experience is with my '95 M-Sport, a friend's '95 525iT, and another friend's '93 M5.
If you'd like some decent pics of an M-Tech bumper go to www.kindel.com/bmw to look at pics of a silver M-Sport.
And if you've already bought the M5 bumper and wanted to run brake ducts you might be able to cut the back off of the blocked duct and hook up the brake ducts from the 540. But I've not tried this out, so I can't say for sure.
Cosmos Black/Black 1995 540iA M-Sport
BMW Individual Exclusive Edition, 1 of 65 total, 9/25/95 Build