I doubt the seller is going to turn over keys to you; you'll have to make arrangements between the buyer & seller.

You'd need to sort out all of that in advance and make your lease really explicit about the arrangement, because it seems like they could be easily taken advantage of if they don't completely understand the setup.  

Lately I have been contemplating the whole "tiny house" takeover.  

Why not arrange for mechanic's lien settled at closing?

I have been contemplating a direct mail campaign, this is great encouragement.Congratulations on the nice investment!

Maybe a credit partner would be the answer I might need to work my network but usually what is a good arrangement / agreement on this situations ?

The arrangements are that he paid for the property and I am paying his loan plus interest.

I see the invite every week and every week I say I'll re-arrange my schedule to go.

Currently, I'm holding a 10 unit building in a LLC and am contemplating creating an additional LLC to hold the title of a 12 unit.

As a contractor, start with a scope of work statement, materials, labor and expenses (permits, trash, etc).State the partnership arrangement, who is responsible for what, when and time lines.You need to state a purchase price, in whole or for any partial interest.Your estimated sale price and how offers will be accepted (generally at appraised value can be agreed to).