Probably not (as stated ask your Immigration Office) as your first Extension of Stay usually requires 800k in a Thai bank unless your Embassy still does the income affidavit
No, a tourist visa gets a 60 day entry stamp which can be extended once for a further 30 days (1900B). To get a stay of 6 months (well, 180 days) this would require at least one border bounce using the METV then another extension.
You've got a 60 day entry stamp, get the tourism extension for 30 days more then get the Extension for Visit Thai Family at the end of your tourism extension to get a further 60 days. These two extensions (1900B each) give you the extra 90 days you require. When you get your tourism extension ask your Immigration Office for their list of requirements for the Extension for Visit Thai Family.
Agreed, and I think the complexity (witnesses, house visit etc.) is for the Non-O based on marriage not retirement unless this is a requirement that Udon Thani imposes.