DLC downloads to your SD card, not the game card. So any DLC you download will forever be accessible in any save file you have. Anyhow in terms of which characters will be available when, I recommend looking at the list of Spotpass character available in the Japanese version of the game.
http://backloggery.com/lunarroar Official Abra of the Pokemon X/Y Boards
You can look at both the Japanese and NA lists here, not to mention get to see which characters are available and what class/stats/skills they start off with.
Bear in mind, as you can see, the JPN and NA had gotten teams in a different order; going by this, it seems fairly likely we're getting Path of Radiance (of which Radiant Dawn is a sequel of, so almost everyone on that list is also in RD) next, then Radiant Dawn after that.
When Snake sees a "!" over someone's head, he runs and hides. When the Pokemon Trainer sees a "!", he beats them up and takes their money.
I can't wait for the FE4 characters. I want to see the localizations, we already have Deirdre, Sigurd and Julia...
Don't forget Seliph and Leif.
....Wow, those two rhyme. (also, YAY for Julia being the official name. Julius is likely as well, and seriously, both of those are WAY better than Yurius and Yulia...)
It was Yuria, not Yulia. Yulia is a legendary hero from Tales of the Abyss, not the invincible goddess of nosfertanking.
And no, Yuria >>>>> Julia, same for Yurius >>>>> Julius. Although, Julia rolls well with Celice's new name.
I hope we actually get them too. I understand them starting with FE7 (since that`s we got first) but no idea what they'll do with FE2-6.
We'll get them at the very least as NoA has advertised the "120 spotpass characters". Unless they plan on making new ones, which I really, really, really doubt, we're getting them. Of course, the idea of "No Spotpass before DLC" is already trashed. (To be fair it was trashed in Japan too. Katarina got a Spotpass... and then was the final DLC character.)
Think a NEXT will save you from BETA? Think again. http://www.fanfiction.net/s/8572968/1/Project-Ignition