Lotsa Q's, but I'll try to answer as many as I can.....
The one-way for the S2 is a drop-in accessory. You don't need anything extra. The rear ball diff, if you know how to lock it, is also a drop-in item. Remember....you will still need to lock the ball diff.
No, the stock springs are much too stiff. You will want to soften the front end, while keeping the rear relatively stiff, but not as stiff as those stock springs.HPI has a confusing list of spring rates for the S2, but when I had mine, I dispensed with the stock shocks altogether, in favor of Tamiya TRF shocks, which are arguably the best on-road shocks you can buy. They are also not direct bolt-ups, so you will need to get Tamiya ballstuds to mount them to the S2. On springs, you will want Tamiya blue springs for the rear, and possibly red springs up front. Shock oil is your choice, but anything close to 30-35 wt will do fine.
On surfaces, you pretty much have it down. HPI's T-drifts are fairly good tires, but there are better out there. I suggest you get as many different types as you can, and experiment. I have used Raikou (raikoudrifttires.com) DXPE's and D70's with great results, Yeah Racing 3 degrees, HPI A-drifts (those are more for nitro drifters, but work on really slippery surfaces), all to good effect.
Camber is a cosmetic affectation. It doesn't do anything for performance, just looks. Yeah Racing 3 degrees will require 3 degrees of negative camber, to get the tread to sit square with the road surface, but in all truth camber isn't necessary, otherwise.
by stabilizer you mean their D-box, forget it. That's $100 you could spend on better things, like CVD's. Drift gyros don't do much to learn drift. They are "cheats" and most seasoned drifters look down on them. It's not difficult to learn the basics of drift, it's the control aspect that will take time to learn. You can do it without a gyro. Check out HPI's drift tutorial at Youtube. (you might have gotten a DVD with the S2, it's on that) Those are the basics, so you can progress from there.
You will not become an "expert drifter" overnight. It takes time to learn, and patience is your buddy, here. There will be days when nothing goes right, no matter what you do. My advice is to put the S2 up, and try again another day, if that happens. No sense in getting frustrated. Just try again later.
I've been at drift for about seven years, and I'm no expert. I just recently got one of my high-end drifters CS'd, and that's a whole other ballgame.
Hope some of this helps you.
