When I paint on base, I don’t sweat the rubbing off of paint: I just carefully touch things up and then varnish: two spray coats, one gloss followed by matte. As long as I give the figures a proper basecoat, I have zero problems with paint rubbing off.
3mm is better in this sense, actually, because the figures are lighter and generally handled by the base. My 15mm stuff gets some wear and tear, but not 3mm!
The broken spears are another thing entirely. O8’s alloy has problems with anything longer and more delicate than Roman pila. How they are going to do pike blocks is anyone’s guess. I have suggested piano wire, but Marcin sneered at that idea.
That said, my Roman cavalry with the long spears are standing up well: zero breaks so far!
For painting faces, I actually use a pretty thick brush. A 0, IIRC. It’s all slash and dot painting, anyway, so if you get a little sloppy, don’t sweat it.
We get slapped around, but we have a good time!