I have 3 temp probes, room, tank, sump.
2 pH, sump, calcium reactor.
ORP sump
Conductivity sump
A few things, in the sump, keep them away from heaters, pumps as you might pick up electrical interference.
Correct no bubbles, but as far as calm, you want a decent flow to go by them. No stagnant areas.
Also if you do run a conductivity probe to monitor your salinity, and if you have one, keep it away from where your ATO enters.