10:1 is the safe ratio, none of the variables being known.
I’ve had success between 5:1 - 10:1. Much higher than 10:1 and you might not hit supersaturation/cold crash ability. Lower than 5:1 and it might not flow through the filter.
As for temps, I like to do a room temp crash and filter, then 0c, then take a small sample and chill it to -20c ish, filter, see if the whole batch needs to be done this cold or not