autox allows even the M2000 helmets, but they do recommend SA2000.
as for open or closed face, they're both allowed, it's personal preference. a lot recommend the closed faced one though (specially for open cockpit cars).
when i did my research, i thought that open face would be alright. but when i was running at the autox already i kept on looking at the steering wheel and how 'vulnerable' i felt my face was. i guess i kinda became paranoid, thus i switched to a closed face. nothing to lose being extra careful