Installation is not difficult VERY similar to painting. 

The most common issue I see is an investor, many out of state, buying properties in rougher neighborhoods because it's cheap, not realizing that it's active income and much more difficult to rent out and keep good tenants but there's also an issue finding legit contractors to work in those areas and they often will charge higher for the risk. 

Difficult in terms of how? 

Basically, he just seems difficult to deal with.

After paying $1,933 a month for three years, I'll still have an unpaid balance of $343,000.

It is much more difficult. 

I believe his loan balance is $125,000.  

And you're too small for the commercial guys to waste their time.The flip side to doing one loan is that if you want to sell one or more of the properties before the mortgage is paid off, that's going to be more difficult. 

I have found it very difficult to find a good agent.

I need a lawyer when we decide to form our first LLC for the rental, and I also am in need of an ambitious tax person that can help us find a balance between minimizing our taxable income vs. investing more money in our real estate portfolio.