The mileage rate also takes into account vehicle depreciation.  

There are mortgages that are built similar to the FHA style (less than 20% down with PMI), buy many/most of the other loan packages will allow the PMI to be dropped after the LTV reaches >78%.While FHA is a great investing vehicle for a new investor, it may not be the BEST option.

We have debt north of 200k to include vehicles, student loans and credit card debt. 

When REI can not compete with other vehicles, like stock, REITs, bond, etc, money will leave REI.There might still be deals out there, for seasoned investors.

As  equity builds I pull it out to invest in other vehicles paying higher returns for diversification and reducing my risk.

This question and the answer can be complicated without knowing your long term goals and investment strategies.You should develop a plan identifying all your goals and what investment vehicles you will use then it would provide you the answers to needs. 

This sounds like your situation.As @Allan Rosso noted, a partnership or LLC agreement seems to be the best vehicle. 

Hard money is a short term vehicle and not something you would want to use to acquire a rental property for example. 

When tenants apply to rent any of my properties, I require them to list their vehicles.

You can obviously modify it to ask for make and model of vehicles.