Cool, thanks. I forgot about free background skills.
As for his power framework, I figure he got sprayed / gasses / irradiated / etc. with some sort of physical enhancer by the shady business guys as part of their secret human testing program, and they're monitoring his team to see what effect it had.
I was thinking of some sort of industrial "glue" that strengthens the molecular bonds of his tissues to make him super strong and tough, or perhaps an environmental fusion with the steel and cement to give him strength from absorbing some of their properties. And there's always splicing his DNA with alien DNA as a possible source of the powers. But being new to the system, I wasn't sure exactly how power frameworks work anyway, and I figured we could hammer it out when we get together. I figure his power framework would include the Characteristics STR, CON, and BODY (and maybe DEX), as well as the powers Armor, Damage Resistance, and Regeneration, which is why I didn't buy him any powers beyond those.
EDIT: That was the idea behind his Susceptibility disadvantage, as well: whatever process gave him his powers involved some sort of catalyst / solvent / byproduct that affects him because of his powers.