Transmissions

Hi, I'm here because my brother wants to turbo his 08' LH6 5.3 Envoy denali.
He asked me to help him find parts because I'm also prepping my ranger for a 2.3T swap and am accumulating parts, and he's upset that he can't yet afford a fancy new Cadillac.

He wants around 450rwhp and a nice street build, he doesn't use his car for hauling or anything, and doesn't need to go 200mph, but he'd like to be able to pass ******** without a problem and think he owns a CTS-V.

So basically, seeing as there's a lot of bullshit on the envoy forums and not a lot of useful things, I've come here. Compared to turboranger this site is massive, which I found while trying to stir up info on LH6 turbo builds. So I figured I'd just ask a couple of questions to get some confusion out of the way for us.

I know what we need for the build but not specifically what we need, so if you could supply a specific part or parameters for a part, that'd be awesome.
Questions: What air/fuel ratio are you turbo guys running?

How much boost am I going to need to get 450 horsepower?

What can the stock bottom end handle with forged pistons?

I think the auto tranny will start to slip so what did you guys use to upgrade?

I'd prefer using the stock cam


Parts list:
T4 turbo .68 ar with waste gate (should be decent)
60lb injectors (dont know what ones will be plug in and play)
Front mount Intercooler (don't know what size to get)
Blow off valve
Upgraded MAF
ls7 springs
Forged pistons
Turbo Headers (aftermarket recommendations would be awesome)
Megasquirt with a tune
Plumbing
Manual boost controller, not sure if it'll be really necessary
Boost gauges
Upgraded head bolts

Edit: I just found the turbo article you guys have written up and reading that before i'm flamed