Your goals are very attainable. It is just going to cost a fair amount.
Go for it!!
I know a couple of gentlemen that have done turbos on 3.6ls. The first hurdle after getting some boost is the compression ratio. 400-425 crank hp is very easy without modifications. If you plan on replacing your headgasket the cometic mls gasket I have recently found out does work. The next problem is that the cylinder walls are very thin on the 3.6. The two high hp cars I know of have gone back to using the 3.2l block with the 3.6 crank. If it was me, I would go buy a 3.2l engine complete from a salvage yard and start with that. Once you get dialed in then you can think about installing the 3.6l crank and going custom rods and pistons. Rods are a must for the end goal. But not necessary to start.
As far as turbo selection, a twin scroll should spool very quickly. You will get lots of input on this subject but mostly it is a lot of opinion, including mine. A gt30 is a good size range, but I might go for a 35. If you get full boost below 3000rpm all you can do is burn outs anyway. Besides even at 3-4 lbs of boost the engine really starts to make some good power.
As far as the transmission. It will handle a lot of power. Turn you modulator up a couple of turns and it will firm up the shifts. I ran mine for 65,000 miles on my blower motor for a total of 130,000 without a single failure.