Looks like the farm is shaping up nicely! Here's a tip on cleaning the rads: save yourself alot of time and frustration and take them to a local rad shop and have them cleaned in their acid tank. It'll come out 10x better than you can ever do at home, especially the insides. Used rads are always caked full of scale, rust and dirt. Then just follow up with a water flush at home.

I got lucky and the stock fans on my car rad undervolt very nicely. I have them running on the 3.3v rail on the PSU no problem and they only draw 20w total. 12v will give great cooling but the fans will suck up alot of power and the noise will be unbearable. You really don't need a ton of airflow so maybe consider something like the 200mm Antec Big Boy fans. They're quiet and have three speeds. I'm using 3 of them on the rad cooling my personal rig.