I try to fly Delta whenever I can (granted, not much). That being said, for our last trip (in June) we booked ~320 days out. Flights were changed, eventually it changed enough that I could "handpick" my way into a better flight. If you're booking a long way out you can gamble and select a cheaper flight that doesn't really fit your timeline, then hope they change your flights and you can select a "better" flight. Again, that's a gamble, but I'd put the odds at 50/50.
As far as luggage fees... if you have decent credit, sign up for Delta's American Express card. You get one bag free for every member of your party. $99/year but 1st year is waived. I got it for our trip and will cancel before the 1st year is up (and then get one in my wife's name... LOL).
As far as travel... no problems. Various planes have various features (ie: online, TV's, etc). That all can be found on Delta's website or seatguru.