This would include doing mainly flips so i can get a solid return from that money or possibly even doing private money lending. 

. - The ultimate house hack, live in the small ADU unit and rent out the two levels of the main house on AirBnb in San Francisco (I would have thought STRs are oversaturated in S.F. but it worked for them and they stay fully booked).

The main criteria is consistency with adopted plans.

You should have two main lessons learned from all this.First: Tenant screening.

If I put myself in the shoes of the outside partner/investor friend, I would be very concerned because: 1) unclear and/or potentially conflicting business plan, 2) even with clarity in the BRRRR business plan, unclear in the viability of pulling it off with these market conditions, 3) the chances of dispute seems very high, especially if you're going to live in. 4 years ago, I went through a  similar thought process when purchasing an investing property with mainly my family money, while considering an outside investor to rehab for higher STR ROI... 

Here’s my two cents:Paying off the condo might make sense if your main goal is to reduce risk and enjoy the peace of mind that comes with no mortgage.

I mainly use FCI and Madison for the majority of my notes.

That tells you mainly want buyers are hunting for and purchasing.

Do you typically have a separate bank account for each property or do you have one main operating bank account? 

If you’re renting an apartment building to mostly Section 8 tenants, the main difference from single-family or smaller multifamily properties is scale—you’re dealing with more units, so you’ll need solid systems for maintenance and tenant management.