Hi Michelle,
1) The average is about 50% acceptance for DW's (varies by group of course, time of year, price)
2) They don't charge open bar per person, since it's an AI. You pay a set-up fee for your ceremony and a set-up fee for your reception, and that includes all food and booze unless you choose to upgrade the food options. There is extensive info on this in the Dreams threads.
3) My deal will be different from yours since we did a vacation package from Toronto. I have no idea what Chicago vacation prices would be like! We did negotiate a group package rate from Toronto though using a TA and then put the info on our save the date.
4) Yes, Oct is the tail end of hurricane season in Cabo, but Cabo rarely gets any direct effects from hurricanes other than rain and wind. I think it rains an average of 10 days per year or less in Cabo. Having said that, we did have hurricane effects (rain and wind) for our first few days in Cabo, which was a bit of a downer. It cleared up for the wedding day though. And we were in Cabo in Oct 3 years ago and it was PERFECT weather! So just depends on your risk tolerance.
5) I would not change any options or vendors. The things that I would change are just little glitches that had nothing to do with Dreams or the vendors I chose!
Hope that helps!