They will put you in the holding room until YOU buy a ticket to wherever they say, or until you can scrape up the money. Many people have reported about it.
The rules do not state a limit, but that doesn't mean unlimited. Visa exempt is for TOURISTS. If you are spending 180+ days in Thailand, you're clearly not a tourist. Therefore it is abuse.
You don't get to decide where you are going. They decide where you are going. They can give you the choice if they want, but they can also make you fly back to your passport country.
Yes. The only person who decides if you are allowed in is the individual immigration officer you are standing in front of. Entry is at their discretion, same as passport control for every country.
There are 3 legal requirements to enter as a tourist:
1) proof of funds (20,000 baht or equivalent in another major currency, IN CASH ONLY)
2) proof of onward travel (a ticket out of Thailand within the number of days you'll be stamped in for, 60 days in most cases)
3) proof of lodging (at least a couple days hotel booking)
Most people won't be asked for any of those things, and they generally only ask if they're looking for a reason to deny you entry or have some suspicion about you.