I tried to do this but credit was difficult to fix at the time.

credit not so good because life lol.

We had to do a full renovation before renting it out, and when we advertised it last spring, we had a lot of applications from people with very poor credit or very tight financial situations.

Why not go back to TD for a line of credit?

any recommendation on who can provide line of credit. rental properties in ohio.

If you try to arrange a seller credit outside the sales contract and out of the lender's view, I think you are playing with fire. 

You can also apply for 2 or more credit builder cards (these often have low limits, and are a great way to quickly boost and build credit).

Because it’s going to cost at least $50 in credit card charges on a $2k/mo rental..Are you allowed to charge extra for credit card payments, say 5% surcharge so people are discouraged?

Fill out an application or complete credit/background check, no. 

with 780 credit and a five-year pre-payment this seems high.