First Ward Sounds brilliant, Josie. I'll help you and Theo decorate, definitely.
And, if I have time, I'll also go with Daphne to help coerce the House Elves earlier in the day.
Second Ward As far as themes go - for Blaise, I would keep it simple and elegant, clean lines, minimal, rich colours...that sort of thing. I can't really think of any sort of real theme for him.
For Daphne, I'd go along the same lines, but add some sparkle. Don't overdo it, but just enough glitter, as she deserves to shine. From what I've heard from Theo, it'll go well with what he has in store for her for their own private celebration.