you must have at least 15 days (21 in some places) left on your current stamp to apply for an in country Non-O visa. If you don't they will turn you away. And to apply online you must first leave Thailand and travel to the country of the consulate you want to apply through
there are only 2 visas that allow you to work remotely, the DTV and the LTR Remote Worker. I understand people work remotely on other visas but not legally so they need to keep it quiet
unfortunately its not how you feel, it's about how the immigration officer feels but given you are where you are I'd suggest a 90 day Non-O based on being over 50 next trip. You won't have any problems with that
If you are thinking of getting back to back Non-O visas to circumvent the requirement to get an extension I suspect it won't take many attempts to find you can't get another one.
You can't apply online from inside Thailand. Go and talk to your local immigration office in Samui about getting an in country Non-O visa as married to a Thai. Take your husband with you
While you need 3 months of statements only the final one has to show the 800k baht or equivalent. Also if one applies for the Non-O based on being over 50 the other can apply for a Non-O as being their dependent with no additional financial requirements