This is where a simple, old school paper application/word document will serve you well. 

You will need to learn how to run comps, figure out what rents are in the area and build connections to PM's, GC's, etc. 

If you have a small multifamily (let’s say 4-family apartment) that has a main common entry door into the building, are you supposed to change the lock whenever any tenant moves and then give all the tenants the new key?

I have a very picturesque property that I have thought of using as an Airbnb type situation, initially with a building not is use....however I am on a creek, with a little dock.

If you just sold the property after building equity then put that money in the S&P 500 you make way more money.

They also haven't kept records of the original origination documents as far as I can tell. 

The reason I ask if it used to ascertain damage to something on the lot (water/sewer/utilities hookups or something) and you don't have pics and mutually signed documentation from the lessor/lessee upon each tenant's move in prior to your ownership, would you be able to justify a charge upon move out?

It's building up equity over the long haul with built-in equity from buying right, appreciation and principal paydown that really builds wealth in real estate. 

I have several clients who flip and a diverse portfolio of buildings.

You will miss out on building relationships with agents that may be able to bring you deals.