Correct: you're only allowed to have the T5 enhs from one tree at a time.
80 APs is the max; if you've hit lvl cap, then there's no more left and you might want to consider respeccing your enhs.
See all the abilities which say "Ranged, thrown attacks, and offensive spells have an extra 7% chance" of doing X dmg? That's effectively free DPS stacked on top of your spells every time it procs. What you'll want is Prism+Rainbow+Double Rainbow+Nerve Venom; all of those have a chance of proccing on every offensive spell you cast. So the basic premise behind most Shiradi casters is max out your proc chances by spamming as many low-SP spells as you can. The drawback is you have to work your way thru the ED trees to get to Shiradi: Fatesinger -> Shadowdancer -> Legendary Dreadnought -> Shiradi. Have a look at the
Mechadi Champion; it's WF and hasn't been updated for the new Enhancements, but the basic concept is still sound.
For now, though, focus on leveling
Draconic Incarnation; in particular, Energy Burst will be your new best friend.