If you leave with a re-entry permit, you can be gone for any amount of time as long as you're back in time to apply for your next extension.
You cannot "convert" to a DTV. Tourist visas are only issued by Thai embassies outside of Thailand. It wouldn't make sense to be able to get a tourist visa to a country while you're already there.
Did you actually come here on a TOURIST VISA, like your post says? A tourist visa is something you would have had to apply for and pay for through the Thai e-visa system before you traveled to Thailand. If you actually have a tourist visa, then you go to Chaeng Watthana.
If you arrived without any visa at all, and you entered visa exempt (free 60-day entry stamp) then you would go to IT Square Laksi.
These types of things are a civil matter, and police don't want anything to do with it. They are most certainly not going to come and arrest you and seize your passport.
I've never heard of a tourist visa not being approved. But most embassies do not require a paid ticket, they just want to see what your planned itinerary is.
For the 90-day non-O visa from the Thai embassy in Canada, you don't need to show any money in a Thai bank account.
But if you want to apply for the 1-year extension in Thailand, you don't have a choice. The Canadian embassy in Thailand stopped income verification on April 1st of this year. So your only option is proof of 400,000 baht in a Thai bank account in your name only.
For Thailand, always print everything. The email you received with your visa should have instructed you to print it.
Hand it over with your passport and final boarding pass when you get to passport control, then when you step away, check the stamp you received to make sure it's correct. Do this every time you step away from passport control.
And don't forget your TDAC when you're 2-3 days away from traveling.