All the 20x12 (and x10) wheels I've seen have a huge offset, they will stick way out. With no lift this will cause you a lot of clearance issues.
Also, will 'probably' not work with those tires. I say probably because you don't specify which tire you are looking at, but it's a pretty safe bet they'll have a rim range that's something like 8-10"
You need to be looking at 20x9s with a 5.25 backspacking. A lot of the 20x9s use a 5" backspacing. These are for lifted trucks and will likely cause clearance issues. Those with 5.5" backspacing will work and if they are too tucked under, you can add a .25" spacer.
All this from my last month of research on this very topic, though I'm going with a bigger tire and a Icon 2.5" kit. I'll likely use the Ultra Predator 8
which has a 5 5/8 backspacing and add a .25 spacer so I'll end up with 5.375"
Though the info should be applicable to your use as well.