New appliances, furnace, central air, and roof.

Well, I've been living in this house for quite a year now, and the Landlord is always being disrespectful with us and always taking too much to fix things in this 10 years old house that is falling in peaces , last week our a.c broke, it wasn't getting cold, so we asked him and only 4 days later someone came to "help", and the a.c. was working again for 2 days, and then it got it broke (the air made an explosion sound and there was smoke coming out of my son's bedroom air ventilation) so we turned the a.c. off and open the windows so the burning smell would go away and then we called the Landlord and told him about what happened and that we need it him to call someone to fix it or something, anything.

The house still needs central heating and air.

The unit dial concept is OK if you don't mind having to replace those that disappear as each tenant leaves.Be aware of the thermal o/load if the fans get too hot usually because something is blocking the air circulation.

As mentioned the legislation regulating STRs in San Diego is up in the air still.

I should clarify a bit, all the homes I've looked at so far have a furnace but no central air.  

They then use a dryer that blows hot air through the bag and it expands, bursts the original pipe and hardens into a new pipe. 

Don't wait for the furnace is blowing cool air when its 5 degrees phone call-- Have a process to make sure your HVAC filters get changed at least a couple of times a year (Don't trust the tenant-- it's your furnace).

In my opinion, spray foam insulation, UV reflective paint, fresh air systems, and solar panels should be standard in all new homes built in the last 2-3 years at an affordable price.

Current property taxes are roughly $1,000/yearCurrent owner pays $350/year for insurance.Current Tenant is paying for electric and sewer (House is on a well, so no water).We think the property will need $10,000 of work to be ready for a short term rental (Air cons, some drywall work, moving/updating the well, landscaping)Our ideal plan is to turn it into an outdoorsy airbnb with a nice backyard feature. 3+ bedrooms in the area go from 60-120/night with ~68% occupancy on airbnb.