I'd like to set up an event for every Monday, except the last week of each month
You can't do that with Google Calendar all by itself.
I was going to suggest setting up three different recurring events, one for the 1st Monday, one for the 2nd, and one for the 3rd. Trouble is some months will have four Mondays, some five. So that won't work.
I think your only realistic option is to create a recurring event for every Monday, then go back and delete the ones you don't want. Twelve events isn't too bad.
For what it's worth, I don't know that there's a calendar system out there that would allow creating recurring events with those parameters.