Oil pressure, oil temp, and boost pressure are the ones you really want as gauges. You want them as simple and plain as possible: Defi ones look pretty, but are not particularly easy to glance over at and work out if there's anything wrong. The gauges shown in the R32 pic are perfect, as they're clean and clear. Plain background, plain font, big red needle.
Things like AFR, EGT etc are nice to have, but really you just want them wired to a single red light that flashes if there is something wrong. In a perfect world of course, really no-one need bother.