Syndicating as a sponsor and making fees for commission plus equity share on the back end.2.

IF they charge you a fee upfront that is wrong wrong wrong. 

If existing tenants were acquired through the purchase of a property could additional fees be tacked on for the use of a parking spot / storage?

Resulting in a lower fee for you. 

What's the easiest way for me to collect a finder's fee/referral fee for helping to connect these parties? 

If you have this, you go down to recorder’s office and pay the recording fees.

This is one time fee.

What do you all think would be a fair fee for something like this?

Just make sure when you analyze the numbers to factor in all expenses (ie. maintenance, vacancy, CapEx, taxes, insurance, property management fees, etc).

Also some damage may not be able to covered by security deposit. 2. more roofs = more capital expenditure. replacing fixtures like roofs/windows etc. costs the same size house, regardless of price of the house3. less able to utilize leverage4. higher turn around with these tenants. if you are using a property manager, this also means more replacement fee for the tenants.One other thing to note is if you can find a home that can be rented for $2000 a month for $200K, why would anyone want to rent that from you?