I have painted many a 28mm army. I use assembly line techniques, simple, fast block painting, followed by brushing on The Dip Technique. It takes a long slog, but when I finish a group, I finish a large number all at once.
I recently began using brush tipped acrylic paint pens. These reduced painting time, per figure, from 10 minutes, down to 5 minutes. It works for me. I have over 1,200 painted figures already. Cheers!