Thanks in advance for any insight :) 

In summary, do you think it's a good idea for me to partner with someone for my first deal, put in some or all of the money, take a smaller return, but gain knowledge and confidence to start on my own in the future?

Even though we'd been renting the house out when we moved away from Arizona, we really never had the foresight to look at the house as a major investment opportunity beyond simply gaining equity each year.

I'm looking for insights regarding creative uses for MR1 lots (currently there are 4 auto repair shops on the 14k+ sqft lot). 

You gained interest/value on pre-taxed funds that you just borrowed from.

Also, you will assume the Basis in any real estate holdings which could have future capital gains implications.Pros.This is a great way to take over an existing loan subject to that would be really hard for the lender to claim due on sale default.

I'm 37, and hoping to get into these houses for long term equity gains and eventual cash flow on new purchases.  

As you gain more experience, your ability to estimate costs will become more accurate.All the best!

What subject to invokes is entrepreneurial risk; the thing all real estate investors live with in an attempt to grow our assets, and gain a financial “free” lifestyle.  

Hope this additional insight helps you in making your decision.