Wow, you have a lot going on in this post!
First thing, you are probably in the wrong place for this type of a dealership. I will try to help you, but most members here are in a completely different space than you are talking about. You will learn a lot here, but may not be ready for so much of it. Don't get me wrong, I am not saying that you aren't welcome here because you are!
You have Facebook, search groups for Independent Auto Dealer groups. You will find groups that are comprised of dealers exactly like you are.
Those banks that you have mentioned there are not going to do you any favors on the type of inventory you are trying to sell. You may want to look into Credit Acceptance Corp. They have a Collection Only program in which they will keep 20% of all payments they collect and send you the 80%. It is sort of like being in the Buy Here Pay Here business without having to handle your own collections.
Craigslist seems to work for some dealers. I have heard selling price is the deciding factor here, but I really don't know. Get yourself a Facebook Business Page, and start listing your cars on Facebook Marketplace. That is free.
If you want to grow this business up into something that is outside of the hobby classification, you need inventory. Yes, you can accomplish this by reinvesting all of your earnings. You can also do this by getting a floor plan. You will hear lots of horror stories about how floor plans have ruined dealerships and that you will go straight to hell if you have one. Floor Plans do not ruin car dealerships. Poor management ruins car dealerships. If you are disciplined and use the floor plan as if it was your own money, you will be fine. Buy cars that are relatively close to retail ready, even if you spend a lot more money for them. The business model you have now will not scale to even 10 units per month.
Contact the Louisiana Independent Auto Dealers Association and become a member. You will learn a lot about your business and market from them. https://louisianaiada.com/
I hope I have given you some guidance here. Feel free to message me or respond here.
Good luck and welcome to Dealer Refresh!
Clint