nope, the normal brush is either too big and have rough fur

Well there are many type of brushes in stationary store, you just have to pick the suitable one. But if you want to paint very tiny part then go for tamiya brush.

not sure if Gundam Marker Eraser works without removing your base paint 
if can't, the other option would be using markers from stationary shops like Artline, Sharpie, etc
it's cheaper than Gundam Marker, and more bling bling, plus can remove using WD40 easily without ruining your base paint 
he did mention he knew about this but it will remove his base paint lol