We are totally planning to visit the monorail resorts to see the Christmas decorations! Brunch and MVMCP are the only things we have planned for Sunday so we have plenty of time to make all the stops. Thanks for the heads up about the party entry time. We'd like to get as much done as early as we can. No plans whatsoever to stay at the party until midnight because we have an early day planned for Monday.I think that combo of activities (brunch and party) will work out perfectly. Might I suggest a monorail Christmas decoration tour in between? That would have been my dream plan, but alas. Also, I'll mention this when I get to my party day, but we were in line at the MK tapstiles by about 3:40, and they started letting us in at 3:46. So if you are wanting as much time in MK as possible, get there early!
Regarding the dress code, I think golf shirt and jeans would be fine for your son (even non-basketball shorts, if he's younger than 10 or so) and nice top and capris or jeans for you. We both wore sundresses and there were people more dressed-up (I definitely remember seeing some of those 50s-style dresses that Disney sells) and some less.
DS is 18 so pretty much grown . . . golf shirt it is. I am a stickler for dressing up for things like this but what I would normally insist we wear is not practical theme park attire. I'm sure after a couple mimosas I'll be less uptight about feeling under dressed, ha ha.