How to structure duplex purchase with someone else that will live there

[NA Ludkey]

My spouse and I are looking to purchase our first investment property - a duplex. Our son will live in one of the units. We will provide all of the financing, but we want him to be a partial owner as his "rent" will go towards his ownership. 

1. We plan to set-up an LLC, is that the correct approach?

2. Since our son will be living there, should we have him own 51% and we own 49% and put the financing in his name (with us as co-signers) to homestead it?  My spouse and I will be providing the down payment.

3. Because we are financing most of it, when there are repairs, how would you factor those costs into our son's ownership?

Thanks for any advice. We've wanted to purchase an investment property for year but have been afraid to jump in. It's time!