Unfortunately for you the Canadian embassy stopped providing income certificates earlier this year so for your extension of stay you need 800k baht in a Thai bank account. For subsequent extensions you can show that you have transferred a minimum of 65k baht per month from overseas each month for the 12 months prior to applying so you need to start the transfers immediately, however you can spend the 65k as soon as it shows up in your account
it will be viewed as a border bounce. If you have zero previous history in Thailand you should get back in ok, but why would you when an extension provides the time you need. Just get the extension
In my view there isn't a huge difference between a single entry tourist visa and a visa exempt entry. When immigration says get a visa next time the generally mean one appropriate for the purpose of your stay
If all that is stopping you is having to put money in a Thai bank then while you are back in your home country get a Non-OA visa as opposed to a Non-O visa. It's good for 12 months (you can actually get close to 2 years out of it if used judiciously) based on money in your home bank, not a Thai bank