I am rebuilding the front caliper and when I removed the piston and seals there is a ton of build up in the seal grooves. What is the best way to clean this out? I was thinking brass wire brush or maybe scotch brite disk on a dremmel?

It looks pretty badly pitted in the sensitive area where the seal goes.  You can try a scotch brite pad and brakes parts cleaner.  But you’re probably better off to replace the caliper.