All resorts are available at WDW with the exception of Jambo House at AKV. Some are only available on the 24th. Some are available for 24,25,26 and some are available for longer.
The date that is more difficult to get is New Years Eve.
But, it is a good idea to get going if you want the room. The 7 month window is not far off. You can reserve now if you have a member with home resort points.
As far as catering, did you want WDW to cater or are you having food brought in? I would suggest you arrange for the rental and in the process have the member ask the questions of member services. The villa accommodates 12 plus 1 child under 3 for sleeping. I'm not sure what the rules are regarding a catered affair/numbers of guests/and other details.
By any chance are you a member yourself? I see that you may be from your signature. You may want to talk to the resort you choose or speak to member services if you want more info. I know that people do host events in spaces such as the restaurants or at BWV, the Attic. There may be other spaces as well. Not sure what a guest count would be for a grand villa.