This is who I used to rebuild my garage back in 2008. They did a great job for me. I don't
know if their still around but here is the info.
Pollack Construction
Batavia IL.
630-879-3933
I had a the same kind of cracks. But I also needed a taller garage door
so I knocked down 2/3 of the garage and rebuilt it. You can see what
was done below.
My garage is 650 sq ft with 9'6" ceiling. I heat it with 45k unit. It should be fine.
I forgot to add garage ceiling is insulated with R-30 and walls are spray foamed.
Al