Not that it really matters, but 10' reduces to 5" in 1:24 scale.
1/4" plywood is slightly less (by about 1/32") in actual size, so this would equate to an approximate 6" wall thickness; however, if you apply sheathing, that will increase scale thickness, significantly for foamboard. Of course, that's o.k. if you want thicker walls.
I personally think 10' of height per floor is good, but there's a lot of leeway to be had with ceiling heights, so is really a matter of personal choice.
One project I tried used Basswood (and some Balsa) for framing, basically as a real garage would be framed - studs, joists, rafters, etc. - and used the same materials, wider and thinner, for exterior siding. The interior was left open, studs visible. It seems you may be after a more finished interior look, though.
Sounds like a great project. Good luck.