20+ (currently 38) but no new parts or mechanism changes except for porkjet's revamped parts (which is a semi-official mod) and Persistent Rotation.
Most of my mods are instruments (KER, DPAI, Better Burn Time etc.) and effects (Chatterer, EVE, Distant Object Enhancement etc.). And I use Module Manager to remove those parts added by mods (like KER) to ensure my crafts are stock compatible (again, except for porkjet's semi-official parts).