As the foundation to the existing garage is not likely to be traditional it s probably a shallow slab a new foundation may be needed for the new wall.
Garage door infill.
There is no standard garage door size.
In fill garage door as part of the garage conversion it is likely that the original garage door will be infilled with a new wall and possibly a window or door.
The interior will be less complicated largely requiring just drywall as a cover.
Remodeling the garage door area appropriately will make the wall space look original to the house design both inside and out.
Our partners at clopay offer custom garage doors in a variety of sizes.
If you need a double garage door the typical measurement is 16 ft.
Specific exterior materials plus appropriate colors will camouflage the opening from curbside.