I do not know what breed, probably a cross and maybe has some Ameraucana in him? I'm not great with breeds though as I just keep silkies.
He doesn't look obese to me. Chickens usually won't be unless fed a lot of treats and table scraps, corn, etc., so not getting the nutrition from their feed. One of the causes of early death is a fatty liver. There are many posts of necropsies done showing all the fat.
He's just simply gorgeous!
The keel bone you should be able to feel under his crop.