I’m trying to figure out if I can wire my current system up to the latest Nest 2.0 thermostat with only 5 wires. In the current wiring configuration, the system is using a HoneyWell THM5421C thermostat which takes 3 wires from the T-Stat and controls everything from a control box mounted beside the furnace. This current configuration does not utilize the HUM terminal on the furnace board at all.

The equipment I am dealing with is as follows:
A Heil furnace, model H9MPV100J20D1
A GeneralAire, model 1042LH Legacy series flow through humidifier (with solenoid and 2 wires)
An AC unit (I don’t believe it matters what the make/model is, other than it has 2 wires on the current system – one connected to ‘C’ and one connected to ‘Y’).
Nest 2.0

My understanding from Nest is that I will likely need to repurpose wires to do the install and get rid of the common ‘C’ connection. If this is the case, I have the following:
1. rH from Nest is going to R on the furnace board.
2. G on the Nest is going to G on the furnace board.
3. W on Nest is going to W on the furnace board.
4. Y on Nest is going to both Y on the furnace board and my Red wire on the AC unit.
5. Spare wire for Humidifier

Assuming this is correct, I’m hoping to gain assistance on how to connect my 5th wire up to the humidifier.
a. I’m assuming I have to use the HUM 24VAC terminal on the furnace, but I’m not sure if I connect that to Nest or connect it to one of the solenoid wires?
b. Where do I connect the second solenoid wire given I don’t have a ‘C’ connection anymore?
c. Do I need to change anything on the furnace DIP switches in order to properly utilize the HUM 24VAC terminal?
d. Am I OK using the HUM 24VAC terminal with this humidifier (ie. is there a possibility of too much current draw?).
e. Which wire goes to the ‘*’ terminal on Nest to complete the circuit?

Thank you very much in advance for all your assistance. This is a fantastic board and I have really appreciated the advice that is passed around.

Cheers.