How many (if any) angels could I keep in a 37g?

4 with a caveat. You need to allow 10 gallons per angelfish. You could try 6 but problems over territory will arise even with 4 if 2 should happen to pair off.
 
yup 4 would be the limit but IMO would press the limit. if a pair form then tank would be fine for the pair.
 
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