First off, you should have never been putting yourself in the position of playing lawyer. You were obviously not suited for it in addition to breaking the law.
Absent an arms length lease executed by the seller, you're a month to month tenant and despite all the "details" you enumerate, the new owner is free to give you fifteen days notice before the end of the subsequent monthly term to have you out (with no cash for keys).

Whether the fact the property rental should have been disclosed to the lender is entirely between the bank and the borrower. You have no bone in that discussion. Consent to lease is routinely given and frankly, if the intent was to terminate the lease and occupy the property, there's no real issue with the bank here. Short term rental after closing whether by a tenant or the former owner (it happens at times when the owner's new property isn't ready, I've done it a couple of times in the past), is not an issue as long as the intent is to owner occupy.

I'm not seeing how you have any recourse here. You can talk about all this intent to elevate your status but it's all talk. There's not anything even resembling a contract here. You are solely a monthly tenant and Florida only requires 15 days notice for termination.