You'll find a lot of the details from last year's event at:
http://www.allearsnet.com/tp/mk/mnssh.htm
"Most" attractions will be open, but not all -- you can count on the premier attractions but not necessarily on the peripheral stuff (and they seem to tinker with it a little every year).
A limited number of restaurants will be open during the party, but you can plan to eat early, certainly, and then hit the party.
Enjoy!