Wow, questions within a question.
I cannot answer about the trucks. ButI can tell you that 1/72 tanks are pretty small - detailing them is a chore. To get the right effect, 1/35 is better simply because a well detailed armor vehicle is rather "busy."
In the small scales, this busy-ness is not only hard to reproduce, but it gets muddled in the overall effect.
Airfix 1/72 kits are of varying quality. If you get one of the newest ones, like the SHAR 1 or one of the new Canberra's, they are quite good, overall. Detail level is excellent and the decals spot on. Airfix has stepped up their game recently and it shows in the model quality. These new kits are normally found in a solidly built, red boxes.
However, if you get one of the boxings containing plastic shot from the old molds (some going back to the 60's), then that is not the case at all. Detail is sparse, panel lines are raised and and the decals may be questionable.
Since you'll be getting it at a LHS, you should be able to specify the new issues and make the right selection.