If you haven't tried the Star TL yet you might not find it to be short. Everyone here says that the X Avenger is longer than the Z, for me the Star TL is on average 10 feet longer than an X Avenger. Way more forgiving to bad technique too.
If you are just planning on buying discs and making up a bag without actually throwing any of the mentioned discs you will be suprised and probably dissappointed.
Heavy S Demons are hard to find. Your firebird and extra height would yield the same result, just play the skip.
If I were you my bag would be:
170 Champ Firebird (wind)
172 Star TL (goto)
Whatever incarnation of the Inferno that has been around longest. (max D)
DX Dragons (water, turnovers, downwind)
DX Firebird (water, overstability)
175 ESP Buzzz (master 1 mid before f'ing with another)
170 S Wizard (E's are more durable but for me they like to eject themselves from the basket on good putts. Plus S is the best plastic in any weather condition. Slippery putter=I'm beating you on the course
I think that a simple setup with discs that get thrown regularly will yield the best results for anybody.