Thanks for the input Rich on the wheels and tires. I forgot about the RS3 -- that sounds like a plan for the time being, so I'll check into those. I do have a set of A6s, 275/35, from the year before last that I could use in F-stock for the first few events and then switch to TIR class once the Rival is available. They've been stored well and have only seen about 10 runs on the M5. I'll have to think on that option too.
Anyway, this is going to be a fun season. I plan to take the car to the next CCA autocross at the Performance Center as I have a history there of three FTDs and one 2nd FTD with the M5, and I'm pretty sure I will be faster in the M3.
I also hope to make it to an SCCA event at the Michelin Proving Ground in Laurens, SC this Spring too in addition to my local club events.