Mainly you're responsible for the sewer bill and to provide heat and hot water, but not things like air conditioning.If this was winter, I'd be concerned about pipes freezing if the relationship isn't going well, but a 10 year tenant probably won't let that happen.I don't really know about the downsides of not having a lease. 

Rather than spend an hour doing something that others consider fun, I spend it on prospecting and educating myself, to me that is fun.

This past winter i signed a tenant for three months with options to extend monthly until spring summer.

It is no fun having a smoker in an apartment!

I wish things like this were a little more black and white, but then again what fun would that be.  

Very few people move out of storage in the middle of the winter and all locations around are full. 

Quote from @Marc Winter: Not sure I understand what you meant:  the TENANT wants to make a deal?

My partner bought a studio, front line to the sea in Costa del Sol, initially just a warm escape from Chicago winters with no intention to make a profit. 

A key part of your projections will be mortgage terms..check in with @Joseph Chiofalo he has a fun comparison tool and my go to lender for over two decades.

My concern is being able to find a tenant during fall/winter months.