I've been doing a fair bit of experimenting with FP4 reversal processing lately. To address the OP's question of over/under exposure - expose correctly for the brightest part of the scene or for your subject if that doesn't happen to be the brightest part. Underexposure (even a modest amount) leads to an overall appearance of muddiness. Overexposure, of course, burns out the highlights. When you get the exposure spot-on, it really shows. Bracketting by half a stop is a good idea if you want to be sure. The last little niggle that I'm trying to resolve is a slight tendency for the blacks not to be quite black enough and to exhibit a dark green hue when examined closely on projection with a 250W carousel. I have a feeling that the cause could be that I'm using well outdated Ilford Motion Picture stock and the faint base fog that I see in normal negatives which isn't an issue and I can print through actually gives a slight lightening of the blacks under reversal. I'm being picky, and other people (non-photographers) can't see what I'm fussing about! Anyway, to try to prove a point I bought a ***NEW*** roll of FP4 yesterday (exp date 2018!) and will try that. My camera won't know what's hit it. I can't remember the last time I used in-date film!
Tom1956 - Yes, there is some base colouration with most b/w film, but a) some films don't have any (as has been mentioned) and b) even base colouration that is visible when a neg is held up to the light has never been a problem for me when projected. I have no issues with brightness with my usual 250W carousel. As donkee says, there is an element of Hobson's Choice. With E6 films fast disappearing, part of my reason for b/w reversal is to maintain the ability to shoot slides. The other part is that a decent b/w slide of the correct subject matter has a lot of impact.
Apart from the availability of colour slide film, the cost of the stuff and of the processing are beginning to make me think twice every time I press the shutter. I can see the time when I'll take two cameras on a trip, one for b/w slides and one for colour. Most of the material would be b/w with expensive colour reserved for subjects that demanded it.
Another option for those of us who like to project images is, of course, to use colour neg film and scan it. A club I belong to (nothing to do with photography) has just bought an Acer video projector using DLP technology. It cost a shade over £300, produces a very sharp, bright picture with auto keystone correction and excellent colour rendition. That and a slide scanner do introduce the 'd' word but do at least allow us to continue shooting film for ultimate projection.
Best wishes,
Steve