Is Summoning really a power though that can be linked with Teen Titans? But I suppose if you make the 'Summoning' all the same thing roughly you can count it as one. Like My characters power is to generate ice from her body. That is just one. But that can be made into weapons, armor, shields, projectiles, Ect.
Just gotta be clever to get more stuff into one thing.
No but there has to be some limit and I'll you decide what that may be, for example if you have a really power summon the rest of your summons might be considerable mediocre. Also you can have two more powers but they have to make some sense like how Athena only has metal powers and not elemental powers and physical power,not to say that you can't try to talk me into having two complete different powers but your gonna have to explain why your character has those powers.
EDIT: Magic does exist in the Teen Titans and even the DC Universe so I'll allow a summoner.