Turn washer spin speed up to the highest setting because they're unlikely to change it..5 GPM aerator on bathroom faucets1.25 GPM aerator on kitchen faucet1.25 GPM showerhead1.28 gp-flush toilets--I'm only replacing them because they're the horrific 90s toilets that clog CONSTANTLY, as the water savings will literally never pay offNew tub spout diverters because the current ones leak around the edges badlyY-splitter on top load washing machine to connect the washer only to the cold supply (it's not a high-efficiency, so it cleans well at any temperature) Smart thermostat with 74 degrees minimum cooling temp and 71 degrees maximum heating temp until 10 pm, dropping to 68 degrees until 6am Alarms on doors and windows that alert me if either is left open while the heat or AC is onNew windows, because the current ones are single panes in need of heavy maintenance and are already causing problemsPossibly solar screens on two of the windows that get the most light, particularly a west-facing one

I am planning to add a bathroom and a bedroom down there but was wondering how I'd go about adding the bathroom since the sewer line is above the ground as won't be able to use gravity to do its thing.The washing machine setup is very weird on that side as the wastewater goes directly into the sump pump, never seen this before. 

If cards are available to purchase for cash then the cash must be pulled from machine regularly. 

I don't think my strategy was to be my own gentrification machine; more important to me was that I bought houses in the geographic area I thought had the best long-term outlook, combined with ease of self-management and homes that fit my preferred tenant base.

@Pedro Machin If it is in FL, the Property Appraiser site has the land/building values shown. 

Invest once you have your machine working.

Storage areas can include built-in cabinets, closets, attic space, and even outdoor sheds, etc.Laundry: Including a laundry area and machines is a big bonus for tenants, as they compare that with apartment living where they would have to use common laundry machines that require payment.HVAC: Make sure to include an effective dual heating & air-conditioning system to service the ADU, so your tenant is comfortable in the unit.Kitchen island: It may be difficult to squeeze in a kitchen island in a small ADU, but it’s a big bonus if you can make the space.

My fear is theft, using each other’s machine, etc.

Like for cleaning feeding tubes, diapering, the air / water dishes for various machines. 

No professional photos.Photos not staged properly (clutter, beds poorly made, etc.)Underpriced, especially for events and holidays.None of the small things that folks notice and mention in reviews, such as bedside chargers, noise machines, well stocked kitchen, local coffee & snacks, etc.