put on the new t.b. now or wait till h/c/i

Putting it on the car will help, providing you widen the opening on the stock intake to match the bigger TB. Use the 70mm gasket as a template to mark a circle around the opening on the intake and then use a Dremel and grind the opening on the intake to match the circle, and make a nice, long tapered transition into the intake. You want to make sure not to get any metal chips in the engine, so its best to take the upper intake off the car while you're doing this, and clean it thoroughly afterwords.

what size MAF you using? like NikwoaC stated it will help some, might feel better throttle responce might not, but it isn't going to hurt anything. The gains will come when you do the h/c/i and the motor can really use the added air.

put it on now. Wont add any HP but throttle response will be snappier.