Hi.
We are having a dessert party and private Illuminations viewing by Rose and Crown in January. The name of the area we rented is "UK Upper Terrace." We made all arrangements through the Park Catering and Event Services Manager, Dante Gibilisco, at 407-566-6482.
The UK Upper Terrace holds a maximum of 50 people, and we needed 24 people minimum to break even for the particular dessert menu we selected (our cost came to $30.15 per person).
One thing I learned in the process is that there are tons of places of varying sizes around the WDW property where one can arrange a private event, and there are lots of choices for food and beverage. Dante can give you the particulars and even send pictures and menu ideas via email.
Hope this helps.
Janet
PS: One thing Dante told me is that you can make arrangements for guests without park passes to be escorted from the gate to your party. There is an extra charge for this, and I don't know the amount, but I belive it is much cheaper than each person buying a park pass.