Meth is simply another way to cool the air that gets put into the engine. It also increases the octane of the gas in the cylinders as the meth cools off in there. I would also suggest wrapping your downpipe and turbo to prevent heatsoking the TMIC. Meth does require tuning, so definitely budget a tune in there as well. Just make sure you either have a guage to tell you how much you have in the tank and/or a map tuned for when you don't have meth. Aquamist has an awesome meth kit that comes with a few failsafe features, so definitely check into them.
As far as tranny and clutch go, this depends on how you drive. Stock can always hold fairly well unless you like dumping the clutch at a stop, which would require stronger gears/clutch. Upgrading the fuel pump and injectors would be a good idea as well since you plan on getting a better turbo.
I would definitely do the 50/50 mix.