Surely the speed at which you play tunes is determined by
1. Personal preference
2. Personal capability - no point in setting it so fast you can't play it!
3. Whether playing for dancing, singing or purely instrumental - if either of the former 2 then go by what your dancer or singer wants: if you use a metronome then adjust it to marry up with your dancer/singer's preference (and maybe record the reading for future use).

The other main use of a metronome is to keep those folk who CAN'T keep time IN time, but they will probably mentally bypass the metronome anyway.
As for tapping, a quietly visible foot to watch is OK, but PLEASE, NO heavy stamping! My metronome is inside my head (no, I don't even have to nod it), not my foot.