If you are buying another home, I think there are also ways to transfer your mortgage.We have mortgages that are similar to that in the United States but use different terms to describe them.

You could build or flip less expensive units and sell them to your clients/occupants over time.

* How do you advertise your vacant units?

Try to find a BRRRR multifamily deal and live in one unit and house hack it then rent the other units out. 

What is your comfort level? 

How do you advertise your vacant units?

You could live in one unit and rent out the others to offset your mortgage, staying within your $4,500/month affordability limit.

Investment Info:Large multi-family (5+ units) fix & flip investment in San Francisco.

On the RE side - I own/developed 2,000 residential units across the United States focusing on opportunistic residential acquisitions and development, including student housing conversions and luxury multifamily development.On the startup side - it is a third-party guarantor platform that expands your renter pool, increases rents and occupancy, and ultimately boosts your NOI while broadening affordable housing options for renters.

You mentioned that you've been paying water / sewer for all 4 units.