I can eat the 3% fee since it enables me to get all 4 units rental ready and get income flowing.  

For investors, if I assume 0% appreciation and a bunch of tenants rights nonsense eating up net profit, the numbers do not work for SF.

The fees are not predictable, special assessments do happen and it simply eats into your cash flow.Second your agent is right you will have no problem getting tenants, getting them to pay and keeping them is another matter entirely.

The buyers premium seems high and  eats into your profit margin. 

One guy I've been with since he started, we have a running joke of it: Him: "I need to eat, is Sally preapproved yet?" 

An upping of property taxes could really eat into your returns.

My guess is, after mortgage, you will be cash flowing about $2000 / month then if not less depending on the terms he wants. that's about $90 / door / month cash flow. i don't own a complex that size but i believe most investors here wouldn't touch it unless it was $100 / door. but if you two are fine with that, i would seek out any family member or friend that would loan you the money, just realize you would have to pay them back with interest, that will eat away at that $2000 making it less.

This could eat into your cash flow.

I always use my right hand to eat.

Yes, dues and assessment can eat up your cash flow, but you also (again, in a good association) are getting something in exchange for the dues dollars such as management, insurance, Cap ex, all exterior maintenance and repair, landscape/snow, common area care, etc...