Well, there's nothing that can't be handled at home, assuming you have all the tools listed in the instructions, and you don't break anything along the way.
The hardest part by far is the up-pipe installation. To have to take off a ton of the exhaust (right side headers, downpipe, and of course the up-pipe). It's a dirty and physical job with all the pipe wrestling that has to go on.
The spark plugs aren't easy like most cars... you gotta move lots of stuff like the intake, battery and washer fluid bottle.
The underdrive pulley requires some serious elbow-grease, even after liberal amount of liquid wrench.
Removing and installing the intercooler requires lots of wiggling and yanking. Especially if you get the silicon pipes like I did.
The wiring and plumbing for the ECU and boost controller is a since if you've ever wired a car stereo. Make sure to get the wiring harness... it's over priced, but without it you can't revert the ECU back to stock w/o repairing some wires.
I'd say on a 1 to 10 scale, 1 being an oil change, and 10 being an engine rebuild, Stage 0 is about a 7. There's lots of things to do, and all of them have their quirks.
I did mine, and it took about 14 hours over 2 days. I could probably do it in around 8 hours now that I've done it once. Actually I had a leak in the up-pipe/turbo joint, and had to re-do the up-pipe (the worst part!!). The 1st time took about 7 hours, the second time was only about 4. Unfortunately, I *still* have a leak!! Make sure you order the big thick gaskets available somewhere on
www.NASIOC.com And when you order them, let me know where you got them, cuz I can't seem to find the guy who's selling them... I think his name's Bill Cook.
So, it's definately possible to do yourself, but it's also hard work. I figured the $700 Diablo Imports was gonna charge me (I think that's how much they said it'd be), plus the time I'd have to take off work to go to the Bay on a weekday, wasn't worth it. Plus it's pretty satisfying to get it done yourself... until the exhaust leaks!
If you want help working on it, I'd be happy to drop by!
EDIT: I just noticed you were talking about stage Sub-Zero, not Stage 0.... you get out of the easy parts... hehe.