Playing a lot (when I am at home) whith 25/28mm scale, I would say that it’s not the best scale for what you attend to do. This scale goes really fine and is extremely visual and friendly used but 3 or 4 blocks means a very large board: around 2x2 metres. This in the idea that you have 4 blocks with let say 3 to 4 buildings per sides.
I would rather recommend that scale for a village position with a 1x1 m board and something like 5 to 6 houses and 1 mosque/church… Plus some surrounding country area.

For what you plan, the 1/72 scale seems the most adapted. Also it will be the cheapest option. You will be able to create your building easily with cookies boxes and beer canes (eat and drink first ) and vehicles are easy to find. Toy cars (matchbox or other brand) for civilian vehicles and miniatures from Heller or Airfix (or any other brand) military vehicles but you will probably have to assemble them.

It is extremely visual and shows well (if you have veteran with you) what does work on paper and not in reality. There is always a crazy angle you find in miniature that basically is blind in reality just because there is a tree, a civilian, a donkey or some garbage some where…

The pb you may find with the 1/72 scale is that players cannot really “see” what the soldiers can see. With a 25/28mm scale, it’s easier for the players to jump in the suite of the “combatant”. This because figurines in 1/72 are too small so you do not necessarily pictures the head of a guy above a wall.
The good point with that scale is that you can find easily civilians by going to the small train section. That you cannot find in 25/28mm (or more difficult).

Also, do not forget, those games are time consuming. Average 30 min/player/turn. With the 1/72 scale you can move a lot more figurines in the same amount of time.

The best would be 10 or 15 mm but it’s a hell to find and it’s definitively not made for neophytes. The visual effect works on large scale operation where you play a division.