The real risk is someone dumping garbage on your land and you have to pay to remove..

I think you may be missing expenses for garbage and utilities.

Garbage, sewer, water... 

I have never had anyone issues or pushback from tenants.they actually prefer not having to pay for their own gas, electric, garbage etc.

Who are the water, sewer and garbage providers to the property, and what townships are your properties in?

I wonder if the OP would like all that garbage littering HIS neighborhood!

So many things broke or needed repair within the first year or so: refrigerator, microwave, dirty carpets ripped up and subfloor repaired, AC compressor, electric panel updated, section of the roof repaired, leaky kitchen faucet, garbage disposal, other kitchen updates...Anyway, I went through just about ALL of my additional savings for these repairs and there are definitely more that need to be done.

You should include rules about, noise, parties, lost keys, local violations about that cause fines, these can include garbage, police calls, sidewalk snow removal if tenants are responsible. 

@Trent WernerCheck out getrefm.com I am not affiliated with them but they have great courses on building modelsThe biggest part of any model is the data - garbage in = garbage out so whichever model you use the key is the accuracy of data that goes into it

I get sent so much garbage from wholesalers thats higher then would even sell on market but occasionally newbies get suckered in and buy from them thinking off market means below market.