How do I set up with our local bank for EFT for those customers who want us to withdraw from their checking accounts to pay for rent?

You may already have your answer by now, but the first thing to do is to contact the customers bank. They generally have a form authorizing the exact amount of the deduction, the account it is being drawn from and the account and financial institution it is being direct to. Each bank will have a similar form, but you may be able to take one form, customize it to include your own information and submit it to each bank to see if they would use it. It happens so much out there that this must be a fairly common request.