The hard part is actually removing the tranny. It's ALOT easier with the engine out of the car....but you can drop the tranny with the motor still in the car too. Just have a few extra hands handy.
Other than that, make sure everything is torque down to spec and in the proper sequence before you put everything back together. And I would advise against lightening the flywheel yourself, unless you've done this kind of mod before.
It takes me only ~30 mins to do a clutch install, with the motor OUT of the car. But takes 2-3 hours with the motor IN. 75% of that time is spent getting the tranny out of the way.