/... I want to call it from the first FSM, and maybe I have another object that after a specific action, I would call it then as well.
Use Send Event. You need to create a Global Transition in your cleanup FSM. You create the event in the event tab, then tick the box next to the event to make it global. You then right click on the action and add a Global Transition. This will look a bit like how your FSM has a "START" above the first action, but now it will say the name of your new global transition
above the action.
Now in your other FSM, you do Send Event, specify your cleanup FSM by first saying what GameObject it's attached to, then the actual name of the cleanup FSM, then enter the global transition you want to activate.
If this doesn't make sense, you should just check Youtube or Google for a tutorial with video/images. It's actually really simple but harder to explain with words alone.
So If I have a loop of 4 events, and in the middle of the loop I call the sibling FSM - by send event? ..../ can I return to the loop where I left off?
I don't get what you mean. Are you thinking by doing a Send Event that you are halting your FSM that did it? That's not the case. It will do that action and just keep flowing through your FSM. Now if you do want it to stop, flow it in to a dead end. Then put a global transition where you want it to continue again and use some other FSM to Send Event to that transition when you are ready.
FSM for cleanup. It never turns off.
Should all FSMs start with a listener of some kind instead of being forced to run by "calling" them in some way?
OK so it is common that you may need your FSM to wait until it's needed. Simply set your first state as blank. Just name it Idle or something, because it's not going anywhere.
Then you make a Global Transition on the state you want things to kick off in. Now another FSM can do a Send Event when the time is right to start it off. Now you can either have it loop from then on, OR, make yet another Global Transition that goes to your "Idle" state, so another FSM can also pause the flow again.
Again, I feel like it's hard to describe this with words. Read through this to get an idea of it, but use a video or tutorial with images to visualise it all. Don't worry, it's very simple and what you are describing is bread and butter for Play Maker, not unusual at all.