It seems like it's something people do on the regular, and the lender doesn't usually trigger the due on sale clause. 

What you've shown here is not really a cause for concern in my eyes, however I see much worst conditions regularly.

I'd focus on getting a better property manager, their job is to shield you from most of these headaches and to prevent them in the first place through tenant selection and doing regular property inspections.

Property Management Company we work with right now to manage is fine with regular rental but I am having hard time working with them on student rental where some of the regular renting rules don't generally apply. 

Begin small by making regular contributions to build your portfolio over time.

For clients you bill regularly, you can schedule invoices to send automatically, so you don’t have to do it manually every time.

Things change regularly and I would truly be interested in hearing from investors "everywhere". 

If after adding the additional monthly recurring costs (electricity, gas, water, internet, insurance, lawn care, snow plowing, etc.) to the standard long-term costs (Mortgage, taxes, regular insurance, etc.) the property won't net at least $100 if I can get the average rent I see on FF for that area, then the property isn't worth more investigation.

Instead, just make it a habit to show up regularly and deliver amazing content.

If you have been using expensive vendors, consider switching to more affordable service providers or negotiating bulk discounts for regular services like landscaping or repairs.