Just to finish this thread off...
I installed the fan controller and relay last night. I did have to add a couple washers as spacers for the light dome to clear the speed controller, but otherwise everything else fit up nicely! I tried it out this morning and wasn't sure the slower fan speed made much difference in either fan noise or shower air temperature. I had my wife turn off the shower light so the fan would kick on full speed and...WOW, It got cold in there quick!
Also, I figured we might have a problem with steam building up during an extended shower. Well, my wife and I both showered and the mirrors and sky lights were still clear of steam! So, I think this should work nicely! I even got credit for at least some WAF.
Thanks for the suggestions.