In general I would expect that the crowds won't be all that bad during your planned days. There might be slightly higher than "normal" crowds on Tuesday (spillover from the long weekend ), but in general Tues to Thur are fairly manageable.
If there is a Halloween party, I would guess it would be either Tuesday and/or Friday. I think the party is great, but a lot depends on your kids and how late you think they can manage. The party runs until either 11:00 pm or midnight, depending on the start time. There is trick-or-treating, character meet and greets, the Cavalcade, the fireworks, dance parties, etc. I recommend checking out the HalloweenTime SuperThread MHP FAQ for more information.