You don't need the DLC to get achievements. Though it can be needed for some of the Battle Of the Bands challenges. Which I haven't played recently, since it's hard as hell to beat 3-4 person bands when you're just playing 1-2 people. We should play together and play some of the Battles. I don't have to win them all. Just fun to compete and see how you can do vs your friends and such.
As for the DLC tomorrow, I'm getting all but the "Melatonin" track. That will put me at around 320 total songs in the game. It's definitely nice to have the variety, but it can be tough to perfect a lot of songs when you have that many. There are always a ton more songs to perfect.
Next week's "Presidents Of The USA" DLC will be good, but I wish they'd offered "Kitties" and "Peaches" to the pack. Also, somebody mentioned on the RB Forums that Lita Ford said she had delivered some tracks to RB, so we may see her in the game in the coming months. Cool!