Best site I've seen on scar prevention and treatment is
http://transguys.com/features/scar-care .
Silicone is the one and only treatment that has any evidence supporting it.
In the "top surgery recovery updates" thread here and on transbucket you'll see how guys' scars fade over time.
The good news is that healing can happen really fast. I had my chest reconstruction two months ago and already the scars are really thin and easily disappear with sunscreen on them. A friend had surgery just over a year ago, and his scars are barely visible now.
Just like with response to HRT, genetics plays a big role. As you are aware, people with darker skin pigmentation have a greater risk of keloids. I don't think there's any way to know in advance how you'll do unless you have had other scars to compare.
What you can control, within your budget, is who your surgeon is and your general health, not smoking or drinking or doing other things that mess up circulation or dry out skin.
Good luck, and if you're anything like me, the surgery is more than worth any scars that result. Sitting here with no shirt on enjoying the breeze with not a single regret. Hope yours goes just as well.