About the only solution I had, while I waited for the promised city connect was regular (every 3 weeks or so) pumping of the septic tank and a jerry rigged grey water system for things like laundry.While this was a costly nightmare on the positive side I learned the value of city relationships.   

You want to increase value, not tank a neighborhoods appraisals.

Living on a sailboat or in a camper can have some issues you won't find in a traditional house-- your "plumbing" situation is not going to be as seamless as what you are use to in a house or apartment... you'll have to deal with holding tanks and sewage treatment and disposal, macerators break all the damn time, 6 gallon hot water heaters, filling water tanks, space is small inside (and often outside), insulation is usually non existent.

When the market tanked (this was Silicon Valley, CA), we didn't raise rents for a few years, and even lowered some rents to current tenants who asked, and advertised vacant units at lower than normal cost - just saying that the fact that you didn't raise the rent for a while may be justified in your case, so I don't think you should beat yourself up over that.  

So, even if you didn't intend to keep the manufactured home, it might be a way to get everything financed.And, if the lot allows for more than one home on it, you could put the manufactured home in an area which would leave space to build your dream home later - while living in the manufactured home, which you could rent out later.Lots of options.But, as I say, even if you can afford to just develop this property as far as putting in utilities and a septic tank, you can probably make a profit.  

I can understand her reluctance to fill an oil tank when she is planning on moving in a few weeks.  

I had a cousin back in the 90's doing the borrow on one property to buy another and so on, and he had a number of properties and when the economy started to tank, all it took was for him to have trouble with one property and they all fell like dominoes, one after the other. 

As others have said, quick swap of the flapper/rubbers in the tank are an easy proactive maintenance (you’ll do it now or at 12am, so just get it out of the way early) Tile concern is less about colors than condition of the ground/stability of the substructure.

After a few minutes I still hear the tank hissing. 

Having never owned fish tanks or birds of any kind, I really don't if its even a thing to worry about possible damage or lasting smells.