it's impossible to get a non-O visa without proof of funds in a Thai bank account. Go to Laos and apply for a non-O there. You should have done it before you originally traveled to Thailand. That's how visas work.
You can get a license from any DLT office. Just make sure you have all the paperwork (Certificate of residence, health check, any other items the DLT you will go to requires).
The Thais aren't helping themselves. If they can't rent their condo they raise the price to make up for not renting it in a while. And then they would rather leave the price high than admit they were wrong and lower it. So they all just sit empty. A lot of newer/fancier condo developments are ghost towns.
As long as you do your part (submit immediately after arriving, go to pay the next morning), then yes it's generally 3-5 business days for non-immigrant visas. But you also need to make sure you amount l account for weekends and holidays.
Marriage visa is 400,000 for 2 months before you apply. Wait until you get the actual visa in your passport (not just the under consideration stamp) and then you can use the money for whatever you want.
Most people that have been having issues are those that entered for 60 day visa exempt, apply for the 30 day extension, and then leave and return immediately.
Based on your 4 months, I would recommend doing the 60 days and not getting an extension. After 60 days do your border bounce and return for the second 60 days. Then if you need more time you can do a final extension for 30 days.