You can get an extension (assuming you haven't already) from your local immigration office. 3 forms to fill out, bring 2 passport photos, a TM.30 receipt, copy of bio page and copy of entry stamp plus 1900baht. (You can get your TM.30 receipt from the hotel you're staying at, you might not need it but it's better to have it in case they ask for it)
it's 1900baht and you should never leave it until the day before as there could be a problem or multiple problems that you need to fix. Most offices allow you to go with 30 days left.
you need 3 years unbroken visa or 1 year if married with a child and 3 years of continuous tax payments. If you decide to go back to a non-o for citizenship purposes you will reset your clock back to 0. If your long term plan is to apply for citizenship then you are better off not changing over to non-b just to change back to a non-o.
You will need give more information if you want serious informative answers. No one can really answer this based on what little information you've given.
my TM.30 matched my address, and my online report was still denied. Like a lot of things in Thailand, sometimes it just comes down to luck of the draw too.