All you need is a single place to track tenant information, payment history, maintenance, and a few other things.

No payment goes out without one signed/notarized.As a flipper you shouldn't need any traditional tools.

You might suggest to him to switch to a direct-deposit method of sending you rent in order to make sure he never has to worry about it again (you might even sort of insist on that.) 

On time payments, late fees, damages, pets, who lived there, dates, amount of rent, and the secret weapon only if they ask (would you rent to them again?)

If you already know the DTI is an issue - imagine adding yet another rather hefty mortgage payment to the situation.  

Hey Gladys, typically, you will need a 20% down payment when buying a single-family investment property. 

However, our current roadblock is that we are a little short on funds for down payment/closing costs for any property.

Excellent tools covering market research, financial planning, and a variety of investing methods are accessible.Examine several real estate investing categories, including multifamily, commercial, and residential properties.

Is down payment normal 20% down or higher? 

You basically step into the seller's shoes, handle their monthly payments, and eventually own the place.