Hi @Sam Bewley and welcome to BP. There are lots of things to consider with your potential deal. We don't live in a cash flow market necessarily, but if you're west of the 5 in North County coastal, you'll be good in terms of natural appreciation. It's just a matter of being able to hold on long enough to see that appreciation materialize.
On the other hand, as you mentioned, it seems like there might be some forced appreciation potential with the R3 zoning and the large lot to consider.
I think it comes down to whether you can sustain the $3700/mo on your own because you WILL have some vacancy to account for while owning it. It's important to understand that those won't be the only costs associated with owning the property either. Make sure in your underwriting you're including CapEx 7-10% of gross monthly income, Maintenance and Repairs 5-10%, and taxes and insurance. I assume in this setup you'll be managing the property yourself but include 5-10% for PM for your exit strategy when you move out and start to rent both the front and back units.
Lots to consider, but if you're diligent in your analysis and the numbers work out, then go for it. Good luck