There is also a horse barn and horse fields that could be rented out, a garage, and several small utility and storage sheds.

Greek Islands and especially Cyprus one will notice every building has a black water tank on top of the roof.. this gives all the hot water one would need.. that would be a nice step forward for desert areas of US.. not that expensive and totally basic.. just a black tank.. on the roof.. gravity floor water in black tank is very warm/hot. 

There are also other potential revenue streams such as extra storage bays and coin laundry in the basement.

Having the units so close together, you can create economies of scale by sharing internet service, sharing laundry service area, sharing supply storage areas, and your cleaners should charge less to clean 2 units right next door to each other.  

I’ve pumped many septic tanks and had water flowing with nobody home.

The amount is up to you.I recently had tenants with a needed  oil tank change out and I credited for lost oil and days with no heat.

If so, join a Real Estate Investing "Meetup" Group (one that doesn't sell anything; more of a think tank model). 

In addition, I always bring in a septic specialist they will look at the tank, field and lines.

City will not allow development of a home on the lot.Rent space to billboard company - Called 2 billboard companiesNOT ALLOWED - city does not allow any new billboards to be erected inside the city limits.Build multi-bay garage and rent each bay out for car storage NOT ALLOWED - local law prohibits erecting of secondary structures without a primary structure.Rent to seasonal businesses like flower tents, local farmer, etc.

In Wilmington as well, working with investor group that looks at SFRs, multis, self storage and MHPs.