For instance, I pay my property manager 10% of rent collected per month. 

I have planned on registering for a business to collect rent for the future, is there a way to fund the construction through a business loan, or is that even a thing?

I have mag locks on the doors and I do the cash collection myself.

And while the GP may or may not have had some skin in the game, I'm sure they collected a handsome fee for 5 years that will soften the blow.

Rent for 1st property collects slowly and that is not including tenant issues etc.

I'd rather collect the payments and interest (backed by real estate) than manage tenants (or manage the property managers). 

Some landlords will push that and your local government should provide methods for auditing.A flat fee system is perfectly legal if written as such in your lease and it doesn't matter if the collections exceed the costs.  

Would it be correct to add the repair deductions on Schedule E for 2019 with no income collected until 2020?

@David Martin it’s from midland funding group which I believe is a debt collection agency.

Do they still have to withhold on rent collection?