You don't need a TM30 unless you are going to immigration. If you won't be going to immigration then don't worry about it.
Otherwise, it's a legal requirement regardless of where you are staying. EVERY property owner in Thailand is legally required to report a foreigner staying at their property within 24 hours of arrival.
Only Chiang Saen and Chiang Khong are known to require one night out of Thailand, not 2. Whether they consider you leaving and returning with a visa a border bounce or not is difficult to know. If you are using a different border, you shouldn't have any issues.
Yes, you get it at the immigration office. Each immigration sets their own policies and requirements so they vary from office to office. Here's a general list of common requirements.
No, you cannot get a 30 day extension to a non-O visa. The only extensions available to a non-O are the 1-year extension and the 60-day visiting Thai family extension if you have a Thai wife or Thai child.
That depends on your immigration office. Some require it and some do not. You would need to check with them.
But I certainly wouldn't be paying anyone for a TM30. Tell the agent that it's a legal requirement for them to do it and you are not paying anything for it.