Good point. While I have come to dislike it as being a bit too random, Blue Max is a good point of entry for new modelers. Many more people have built plastic models than have painted toy soldiers, also plastic models are often easier to find in a local hobby shop than lead or lead-substitute miniatures. Also, the norm for new players with this sort of gaming seems to be one vehicle per person, which may be less overwhelming than several battalions/regiments/brigades of troops on the battlefield.

It is asked: What about figure scale? 2mm is easy to paint, but...

Hair-roller armies: More seriously, smaller is easier to paint, but I think that you are right that too small just will not have the visual impact. 25s are commonly painted with quite a bit of shading and detail. I know that I left miniatures painting for some time because I couldn't get 25s to look right. 15s can be shaded, but don't look too bad even if colors are just blocked in, so that's where I would probably recommend starting. Additionally, 15s are commonly available for almost any period.