Typically a duplex will offer twice as many problems that could arise. 2 kitchens, 2 bathrooms, 2 water heaters, 2 furnaces and 2 tenants.

Water heater is not installed, (It is just sitting on the kitchen floor)2.

I mean changing furnace filters, water filters, yard/lawn maintenance etc.

The end goal is to have have to have enough parking for a single vehicle per unit, to separate the water and electricity, and to convert the single family into a duplex. 

However, this gives little wiggle room and I'd much prefer to find a way to make the tenants responsible, not only because it will reduce my costs, but also because it will reduce overall usage and be much more Earth-friendly. 

If you bumped each of those up to 10% as well, I wouldn't object.I'm also curious whether you're sure about the electricity, water + sewer, garbage, etc. 

We inherited a tenant that wasn't paying unusually high water bills, and ended up leaving and breaking the lease in September.

This home features brand new Flooring, carpet, brand new kitchen, all wood cabinets with soft close drawers and hinges, quartz countertops, new stainless steel appliances, new fully finished bathrooms, new interior and exterior paint, new central HVAC, new dual pane windows, new roof, new water heater and all new lighting throughout.

We've owned many 20 space parks over the years, and the key items to consider are:1) They can be hard to finance2) They can be hard to sell due to scale3) They can be hard to manage since you can't afford to hire very good talent4) They are too small to weather any big hits in cap-x issuesSo for this deal to work you'd want to have closer proximity to the park, city water and sewer, and no POHs. 

Depending on the size of the water line needed, the cost would vary.