Two notes regarding Delta...
Bag fees
If you want the 'first bag free' for you and 8 members of your party, sign up for the Delta American Express card. There is no annual fee for the first year. If you are a Delta Skymiles member, signing up for the card can get you 20,000 bonus miles. Simply get the card, associate it with your account and presto, first bag free. Just cancel the card before the year is up.
Flight changes
As mentioned, the earlier you book the flight, the more of a chance of Delta making changes. But, that can work for you. We booked for our trip this year ~320 days out. $144 RT! The price NEVER got close to that. I originally booked a flight leaving home at 6pm, arriving in Orlando at 10pm (because it was cheaper than the flights earlier that day). Of course, Delta changed the flights, so I picked out another flight (leave @ 2pm, arrive at 7pm) and got moved to it with no problem. The downside is Delta doesn't contact you with the changes. You need to keep checking the reservation.