It has been many years since I've used an coin operated washer or dryer, but they used to be able to adjust what the amount they charged by putting something in the slots. 

That way as you grown and if you need someone to take over that part of the business, maybe they can slot right in.Quickbooks seems to be the #1 recommendation, but I'm sure there are others.

If it's occupied, knock on the door.If it's unoccupied, tape a letter to the door (or slip one underneath or through the mail slot if equipped.As suggested above, talk to the neighbors.Ask at the post office what they know?

Today was slotted mainly for phone work.

I am not looking for a lockbox with a single code. i.e. each prospective tenant will show up at the house, after being verified,receives an their personal code which is good for that time slot of say 20 mins.

Because of this, you have just opened up 1 or more slots available for additional Fannie Mae financing.

I agree house hacking a 4 plex to start with minimum down is the Highest and best use of your FHA loan slot..  

Half of them don't show up typically, but at least I'm not sitting around the property waiting for the next 30 min time slot to come.

Every time slot during the day has a purpose... even if that is just free time, social time, family time etc.

It's a shot in the dark and if someone else is paying I would slot up to 7 years owned.