I built this same thing about 15-20 years ago, there was no plaid so I just had them input their routing and account info, I could print anything I wanted on the MICR line so I don't see why you need access to a user's bank account (seems intrusive to me). Also, at that time, I had trouble getting people to pay me even enough to cover postage so bravo to you if you have people paying you $7/check.