I have the below rule to circulate air when the upstairs temperature gets to high when I am home. Problem is that its an OR rather than an AND between the 2 conditions. Also, do I need a second rule to put the fan back in auto mode when the temps come in line?
I'd recommend setting the event trigger as temperature changed rather than a specific value. You can then set the value threshold in the actions to be evaluated, including and else for turning it off again.
The way I've thought about new RM4 rules is the event trigger includes reasons to evaluate a rule (i.e. temp changes, motion changes, etc.) w/o being too specific on what change occurred. You then set the desired values in a conditional action that can be as simple or complex as needed.
Here's a recent thread with related information.
If you're in a humid climate and running AC otherwise, this may not get the benefit you're looking for. There's a lot of condensation left in and around the evaporator after the compressor shuts off, and running the fan puts all this moisture back in your house (which you already spent a lot of energy removing). However, every house is different and if it works for you, go for it!
I have been really happy with having a room sensor (in our case, Ecobee) in the bedroom. It helps a lot, but is only curing a symptom of needing to air seal and insulate the attic.
We're in the Denver area which is pretty dry, the nest rarely shows greater than 35% RH. I have been doing this manually and it makes a huge difference on the comfort level on warm days. It's 84 upstairs right now and 72 down stairs. If I owned the place I would look at a proper fix but its a rental. I suppose I could add humidity to the logic.
Eh my point is probably moot then. CO is one of my favorite places to visit because the low humidity is such a stark contrast from what we get in the mid-Atlantic, where it's an eternal battle to keep moisture out of the house.
If the HVAC fan isn't too noisy, have you considered simply configuring the Nest thermostat to run the fan 15 minutes out of every hour, whether or not the AC/Heat is running? I have done this to help balance temperatures across various rooms in the past. While it doesn't utilize Hubitat, it does take care of itself.