tetras are ok with angels while the angel is small, but some angels can grow into predators of these smaller tetras such as neons and glolights.
if you get another angel make sure it is the same size or slightly larger, as the one you have now will have marked the tank as his territory and may not be too happy about another, and i would suggest getting two more to break up any aggression as cichlids are prone to territorial disputes.
when they are a bit bigger you can resell one of them back to the store.
as for tank mates, theres not many that wont nip the angel fins but you could try red or black phantom tetras which seem to leave them alone.
angels need 10 gallons each and a high tank no less than 18 inches deep for the fins to grow.