not every office can do an in country Non-O visa, I don't know about that office. The other requirement is you have at least 15 days left on your current stamp (21 days in some places) but this shouldn't apply to you as you've not long entered.
there's no chance that even a treatment plan will work if it only consists of 2 hospital visits. You're going to need multiple visits over a period of more than 6 months
there is no requirement to get an extension. But its not going to take the embassy long to work out what you are doing and I'd be surprised if they would continue this indefinitely. It used to be possible to get a 12 months multiple entry Non-O but this stopped when they moved to online.
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