Always keep everything for at least 5 years, you can also scan and keep under a special file for your purposes. 

I can add pics if allowed

You can go to Home Depot and scan all your keys, name them in the app.

This comes as a QR code that they can scan once they receive my letter/postcard.

Hi Alex,At first I was using Avail.com to help me out with putting the pics of the unit, gather information of the apartment, and from there it would also help you and give you lots of advise on how to screen future tenants.

This pic reminds me of your new acquisition.Things were so much different when the first owners moved in.Big carriages and horseback riders.

The 2nd one was more complex and recent, much more paperwork, pulling comps, and showing interior pics.

Pic attached up upstairs floorplan. 

Some pics I have seen of younger ladies seem to express that they might be looking for a date than a property, so it needs to be professional and in good conservative tastes.

Note: for the one that may think this is not ethical, at the register I tell the cashier I got a discount from the manager and I'm applying this 10% coupon on top, when they scan it, it goes through, so "I tell them".