Keep in mind that angels will eat smaller tetras so if you have anything neon-sized, avoid angels. Also, make shure your tank is large enough ebcause angels grow quite large and can be rather territorial when breeding (30 gallons is the accepted minnimum for 2). In terms of the tetra aggression, you should deffinately get a few more to calm things down - angels are often nipped by things like buenos aires tetras but they should be fine if the tetras are in a relatively large group.