I did a extensive amount of research on note investing and wanted to see if anyone would be willing to share their knowledge with me on my first note purchase, which I aim to do within the next 30 days; holding me to a strict timeline will force me to take the leap of faith.

To answer your question she is looking for a flat fee of 10% of the monthly rent collected as the total PM fee. 

Or, I know there are some landlord apps that include collecting rent via their app. 

You collect your fee and that "new buyer" completes the transaction with the seller.  

Check Airbnb for areas in which they collect and remit your local taxes for you.

It will also assist you in collections should you need to go that route. 

I have been renting out my previous home and with the rent I am collecting, I am netting approx $500/month on top of the mortgage (3.75%) and other expenses.

Number 1 I won’t have to bill the tenants and try to collect.  

I scrambled to find a national bank to act as a backup lender and asked the seller for an extension, which they graciously provided.

Can they ask for the rent that was paid during any of this time or try to start collecting the rent ?