Reverse is not midi-mappable. 128 & 256 have a way to reverse from the grid itself, but 64 currently does not (most likely in the next update)
What do you mean by keymap? standalone?
Normally you would either have the quantization on 16n or off (unless you’re working at really fast/slow tempos, in which case 8n/32n might be useful. Are you saying that if you select 8n, it doesn’t become selected?
The grid setting only affects waveform selection in “snap to grid” mode (has nothing to do with the size of your monome or the number of steps). Choose snap to grid, then try dragging across the waveform. you’ll notice the start/end points snap to grid markers now. the grid setting determines the number of grid markers.