I have never bought land on contract, so I probably don't know what I'm talking about here, just a few things that I have questions about.
He maintains possession of the property throughout the term of the contract, only transferring the deed when the final payment is delivered. You would not be eligible for a landowner tag on such a property (you don't own it, you don't have a tax id to register it with the DNR and you don't have final say how it's operated/farmed).
i believe if you are buying the land on contract you would still be able to get a tenant tag.im sure he would give you the parcel number.if not they are online.