Must be over 21 years of age.

IF you just avoid the protected classes you should be fine - age, race, religion, etc.I have in depth conversations with renters to get to know them better.

Mostly jeans, work boots etc, middle aged working class from what I notice touring that neighborhood.One concern is the lack of documentation/ non-notarized.

Depending on the sizes, ages, conditions, and demand, the price and terms will very when you resell them.If you do have to move the homes then this changes things considerably.

I would like to take an aging house, force some equity and cash flow it.  

At our age it seems silly to have taxable investments, since 59 1/2 is soon.

Brilliant decision getting into real estate at your age, I purchased a multi family when I was 19 and still in college, my tenants paid my mortgage and I basically lived for free and it was the best thing I ever did.  

At your age, us that money to put down on a SFH and then rent the rooms out to your friends and let them pay down your mortgage.

Also, depending on the tax bracket and age of the seller it might be worth exploring the option of the 400,000 being paid  as a consultant days during certain revenue benchmarks  or occupancy benchmarks bench marks being met.

Your young age can be a great asset, use it wisely, ask many questions and LEARN.