wow.. a lot of questions :smileyhappy:
anyway, here is my 2 cents:
1. You are correct... ACD groups are the way to go... you would play the regular "business" recording when the caller hits the AA, then they go to the ACD group and you can set up recordings for that.. closed recordings, even "time in queue" recordings. so, customers would hear the regular greeting at 7:30, dial into sales, and then hear "salesis closed, our hours are 11 -2 because we are sales people"..
2. In your Auto Attendant, just have the 1 marked "reserved indialplan".. this will do, then you can record, "if you know your parties extension, dial it now".. they would dial 1xxxx and that hits the dialplan and dials all users beginning with 1.
3. The easiest way to change for holidays (others may disagree) is to go into your Business Hours and set them for the week... so you would be closed on Thanksgiving.. then the system would play the closed message (no special message for the holiday, just the regular closed message). I think that is the easiest without screwing around with dialplans, etc.
your idea for number 3 will also work !!!
Hope this helps !