I haven't seen any announcement to say it's been extended. If no announcement then today is the last day and you're not eligible due to the volunteer visa you had.
yes at the embassy or turn up ay the airport and do a visa exemption. The arousing suspicion would only happen if you do that repeatedly over a period of time.
if you get a visa from the Thai Embassy then yes. If you do it often then you may get asked questions at some point if they suspect you're living in Thailand on tourist visas.
There's no visa for the self-employed so you'd still be stuck on a tourist visa if you don't meet the requirements of any of the non-immigrant visas.
To work you would be required to be employed by a Thailand based employer, yes. I don't know what you do for work but there are jobs here which foreigners aren't allowed to do:
If he's still on the visa sticker then he can resign and that sticker will remain valid until the 90 days have lapsed.
If he's on an extension of stay based on employment then it will be cancelled the day his employment finishes, as well as any work permit he has. He will then need to leave Thailand the same day his employment ends.