I don't have XBox Live but I'm curious, how long do these downloadable episodes take to download? And how much do they cost? And how long do they last?
Since I don't know what type of connection speed you'd have, I'll answer the first question with the size of each DLC.
Warden's Keep: 126mb, $7. An hour or so? I'm not sure because I played through this one as a "regular" part of my DAO runs. I got this one for free due to having pre-ordered, if I recall correctly. In addition to the mission, it comes with a damn useful "party chest" with unlimited storage when your character's backpack is full.
The Stone Prisoner: 197mb, $15. Every new copy of DAO comes with a redeemable code for this one, so it would end up being $0. Comes with two missions and a fully-voiced character for inclusion in your party. First mission could be done in less than an hour, second mission probably a little over. Like WK, I played it as a normal part of the game, so times are estimates again.
Return to Ostagar: 134mb, $5, probably a little over an hour. Played it on its own & in a normal run back when it first came out, so memory is a little fuzzy (definitely better, storywise, within a normal run, though). Provides closure for the slaughter at Ostagar at the beginning of the game.
The Darkspawn Chronicles: 345mb, $5, about 1 hour and 30-40 minutes.
Leliana's Song: 471mb, $7, roughly 2 hours.
The Golems of Amgaark: 421mb, $5. Until today, I had forgotten this came out early last month, so I haven't played it yet. I have read that it is the most difficult of the DLC; in fact, the XBL and in-game descriptions recommend it for experienced players only.
Witch Hunt: 447mb, $7, roughly 2 hours. Could have been a little bit longer, but there was one sidequest I didn't finish. This is my favorite of the post-release DLC, not counting the expansion.
Awakening, the expansion pack: 1.88gb, $30, 12 hours approximately. Since it's an expansion, instead of DLC, it can be downloaded through XBL Marketplace or via a retail store. Does not have to be installed to hdd to play, but I included the size anyways in case you were wanting to download.
You do technically have Xbox Live, by the way, anytime you connect your Xbox online. You just have a "Silver" account instead.
For what it's worth, I've loved all of the DLC because I enjoyed the hell out of DAO. If, however, I were asked which ones could be skipped, I'd have to go with "Leliana's Song" (even though I adore Leliana, it really is just getting to play through the story she tells you during DAO) and "The Darkspawn Chronicles" (since it's not directly related to your Warden, as an "alternate universe" take on events). "Warden's Keep" is worth it for some more Warden history; "The Stone Prisoner" is worth it because Shale is awesome (plus ancient Dwarf and Golem history); "Return to Ostagar" is worth it so long as you take Wynn and Alistair; "Witch Hunt," as I already said, is my favorite. I also quite enjoyed "Awakening," both as a continuation of the story of my Warden and for the opportunity to create a brand-new Warden trying to take up where my Warden left off.
With "Witch Hunt," you are able to import your Warden from DAO, from "Awakening," or create an entirely-new Warden (still the Warden-Commander of Fereldan, as you would be in "Awakening"). I imported my character from "Awakening," since it felt the most appropriate considering the expansion takes place after DAO and "Witch's Hunt" is supposed to occur about a year later. Unfortunately, despite having performed the ritual with Morrigan prior to the Battle of Denerim, that piece of data did
not carry over with that import; she seemed to think I had rejected her, and I think that made me miss out on some interesting dialogue. I'm going to have to try to play it again this weekend with just the DAO post-coronation save instead. Not the first time, incidentally, I've had an import problem in this series. When I imported my DAO character into "Awakening," it seemed to think I had made Alistair King, when I had most definitely chose to put Anora on the throne and become her Prince-Consort. Ah, well, still loving this franchise.
Hope this helps!