What if I get a bigger Clown Trigger then my Picasso?
You're taking an already volatile situation, and making it worse.
If you get rid of all of your smaller fish, then we can start entertaining the though of an aggressive tank. Although that's not really the best plan for success.
What you want to do first is pick either the Picasso, or your other fish. If you don't, one day your Picasso may very well make this decision for you (by killing the rest).
Do some searches, and you will find many people saying their Picasso has recently gone blood-hungry, and that they need to trade him or give him up ASAP.
In any case... the last thing you want to do is add
any size clown trigger to the current mix!
Spend some time on LiveAquaria.com. Browse the fish, their adult size, minimum tank size, and the compatibility chart. The chart isn't the best, but it's a good starting place.
Another great reference you should pick up without question is "Marine Fishes". It's a must have if you plan on staying in the hobby.
http://www.directtextbook.com/prices/9781890087388
Read it through a couple of times, and I bet you'll start to second guess choices you are considering, or have considered in the past.
Another excellent reference is this:
http://www.directtextbook.com/prices/9781890087999
There is also a cheaper paperback edition.
I'd hold off on any new purchases until you pick up either of these.
The worst feeling is buying a new fish that disrupts the tank, stresses out the tank, and handcuffs you with regard to what else you can add later on.