At a guess your UK passport holder, so you can only go the 800k per main visa holder to qualify for visa and first extension. To move to the 65k monthly method in the 2nd year, you need also to transfer 65k+ from 1st month of moving so you have to maintain both methods for the first 5 months. Then just 65k+ for the rest of the year to get yr 2 extension.
groups of people can meet and discuss issues, etc informally aka social gathering. But, the services i assume can be the physical output of the meeting, but i have no idea what services you had in mind. But running a play group, or after hours school group came to mind.
My belief is that if you keep these as social gatherings, then there is no need. If they become formalized, then legaly yes a WP is required. The requirement would probably more about the 'services', as these could be deemed as requiring WP especially if the provided 'sevice' displaces the need for a Thai worker.
Technically your tm30 'check in date' should always be greater than or equal to your tm47 'arrival date', to fulfil one of the 90 day reporting requirements.
because it has nothing to do with the visa, its a totally seperate law, and they didn't send you a document with the 1000's of other laws you have to adhere to either.
When you say it closes, what actually occurs,? If your applying for a non O based on retirement, its design is for someone who wants to retire here and will extend to the full year during that 90 days, and therefore an exit date isnt really required.
if it mentions BOI, that sounds like your looking at an LTR visa, opposed to a normal non O based on retirement. The LTR is expensive and has high qualifying factors, but in the long term a better visa, hence the cost.
for the dtv and the tourist visa when making the application, yes the flight into Thailand must be filed as leaving from the country in which the embassy application is made. But as Brandon said, you don't have to stick to the info you supplied for the physical entry. So you can enter on exempt, then receive your dtv, and at your leisure (within the 60 days of your exempt) pop over a boarder and return with your pdf visa to activate it. Or even leave Thailand in 60 days travel the world for a year and come into Thailand anytime in next 5 years (as long as hou havent lost your pdf) to activate it. The downside of coming when the dtv is still pending is they may ask for more info that you can only supply from the UK, eg copy of p60, copy of utility bill, etc.
400k is the absolute minimum at any point in the qualifying period, you need it to be say 420k, and then on the day you can do a withdrawl of 10k without any worry and enough to cover any bank charges that might pop up during the book refresh.