Nathan, homeless pop up everywhere. There is a very high end gated beach community near me that has a big problem with them sleeping on the back porches of 7 figure homes.
As to the security. SImplysafe is far and above your best solution. Don't waste your time or money with the window sensors or anything else. You will need a base station, control panel and one or two motion detectors. This is what is so great about simplysafe. There is no required contract. Buy the system and put it on your closet shelf in a plastic tote. When your property is vacant, install the system with a little two sided tape, call simplysafe and turn on the monitoring. Set the alarm delay to zero seconds and no audible alarm in the property. The second someone opens a door or window and attempts to enter. The PoPo and you get called. You can use the smartphone app to disarm from anywhere whenever a contractor or someone else needs to enter. The intruder never knows they tripped an alarm.
When all is said and done and you have a new tenant, but the system back in its tote, turn of the monitoring and forget about it until you need it again.