Do it right, do it once. Anything that is easier to do without a drivetrain in the car should be done now. Chances are you'll want to do it later, but it will be far costlier later what with a drivetrain in the way.
Mounts, downpipe, clutch, flywheel.. do it all if you can.
My 2.5 had an 11lb flywheel, and when it was converted to an STi V I had a 10.3lb JUN ultralight put in. Trust me, these are essential mods.. once you have driven a car with a lightened flywheel, you will wonder how anyone can drive one of the stockers. I seriously have trouble with my wife's WRX.. the stock flywheel is so damn heavy that it's virtually impossible to shift slow enough to be smooth..