Specialty advisory firms create these plans, and simply use one or more custodians as the back-end reporting layer.Similar to the IRA is the Solo 401(k). 

What key factors should I consider to determine if this is a good deal or not?

Do you run test ads for the imaginary apartment? Do you run some for apartments and some for duplexes to find out which gets a better response?

I have 2 acres in a rural community that could be used as mini storage ...

Plug your numbers into this pro forma, see what your estimated profit will be, then use the local cap rate to determine how much you should offer for the property.

By having all of the funds in one place, it seems like it would simply things if when I want to say sell some of my rentals and invest in something more passive like a Syndication.

Have exit strategies, Try to determine your "fire sale" price, check rental rates in the area and talk to lenders early in the process that might refinance so you have some backup options.As for DoHardMoney.com, Sounds too good to be true to me.

We are having a hard time determining how to structure the partnership.We have the deal, and some limited experience in a different market (2 years and 4 units over 3 properties in Augusta, GA).

If they're owned by another company you may reach out to them and determine what their intentions are for the home, maybe they recently purchased to rehab which could be great for you. 

I strongly urge you to get a good mentor as well.So, I would suggest that you save those dollars while you explore real estate and determine if it is right for you. 

Also, how can you strereo type me and my ability to construct a deal simply because it’s my first REI deal.