i had 6 emps in a 10 gallon :p depends on how much substrate and hides you have, the more the merrier
got 7 in a 30ish gallon now bout to add more hides and make a hill for them to dig in, planning on going 10-15 in there.
I use a 50w IR bulb in there and its fine, they can be fine with room temp too.
you are local i see, nice to see another scorpion owner in the area lol