I think you prepare yourself for the MC by going over the things you need to happen for recovery...i.e., the things Dr. Harley recommends in SAA. Review the "Four Rules To Guide Marital Recovery" he sets out, beginning on page 87 in that text. You have boundaries and you want to be included on family decisions rather than him announcing them to you. In other words, POJA should be the rule.

Also, I think you should also prepare yourself for your WH to use at least the initial sessions to unload a lot of frustration and pain. Remember, your marriage has not even slightly recovered from your affair and the reasons for it may need to be resolved before you, as a couple, can begin working on the issues relating to his.

Hang in there through the anger. You've done very well just to get him to agree to MC. Stay patient through the first few encounters and I think you'll be well rewarded in the end.