I'm not sure if reservations are required or not. I've always been able to walk up and get a table within 5-10 minutes. However, it probably does not hurt to have them. I would try calling the Disney dining number (407-937-3463) and find out.
For what it is worth, I normally don't bother with reservations ala Disney (Priority Seating now known as Advance Dining something or the other), except for Hoop de Doo (which is a confirmed reservation) as we usually go in August, and as a party of 2, have never had a problem with getting into the restaurant of choice. This year we are going in June and I've made more of these PS/ADRs than I ever had before.
Back on topic and an attempt to answer your other questions:
Attire: we were definitely there in park attire on some visits; on one visit--we dressed up a bit, as we had finished up with services at the spa--and tacked on tea as a post manicure/pedicure treat.
I think the glass of champagne, tea, sandwiches/pastries cost around $21 or $22; and the kid 'tea' was between $7.95 and $9.95--I don't remember. Here's the link to the allears site, click on the tab for restaurants--hopefully you will find current pricing there.
http://www.allearsnet.com
The scones and clotted cream are really, really good.
