serious upgrading going on here. I can get my hands on an auto dim rearview mirror for my max which of course doens't have one already. Is this really beneficial? I guess it needs power, would i need to worry about my wiring harness?

BTW, can anyone tell me if a 2001 manual climate control unit is compatible with a 2000's?

 

1) The auto-dim mirror only needs power (preferably, +12V switched to ignition) and ground to make it work. Yes, it's more beneficial if you don't already have one.
2) If both climates are both manual, I don't see any difference between the two.