We are going to do three days in the park, Monday Oct. 8- Wed Oct 10th. When would you suggest as the best Cars Land day (with the knowledge that Oct 9th - Tuesday- is a halloween party night).
I'm not sure, but someone will correct me if I'm wrong. I thought in October, Cars Land is slated to have early entry for Disney hotel guests on Monday, Wednesday, Friday? If that's what happens, then if you are staying on-site, Monday and Wednesday will be best, provided you arrive at the gates more than an hour before park opening. If you're staying off-site, Tuesday is best (get to the gates well before park opening anyway).
By October, crowds COULD be a bit less, but we don't quite know how that will pan out yet. Currently one possible strategy is to go to Cars Land first, ride RSR if it's running, ride Luigi's Flying Tires and (if you want) Mater's Junkyard Jamboree, and then send someone back to wait in line for a FP to ride RSR again. I think currently as long as you're in line for the FP before the park has been open to all guests for an hour or so, it sounds like you'll get one; it'll just be for later in the day.
I'd ask again in late September to get better information.