In any digital gear I usually leave around 15% headroom. So far the OT runs at max 110 per track.
Seems to work nice enough although I’ve not maxed all tracks and the master to see the result…
As for matching kit, hmmmm, tough one really as fx, samples, mod envelopes etc are always going to affect your volume anyway. You could get an idea of what’s a decent match by using an external program to match dB levels, personally I’d just use my ears.