Play solo mode to earn.
Yes. Rock Band 2 songs work with Rock Band 3. HOWEVER, you can NOT use Rock Band 3 songs in Rock Band 2, and DLC released after the release of Rock Band 3 will not work on Rock Band 1 or 2.
84 songs are in Rock Band 2.
No. Rock Band songs only work with Rock Band, and Guitar Hero songs only work with Guitar Hero.
No. The only way to download songs for Rock Band is through the Rock Band store.
Yes, but only Family Friendly songs are playable.
There are 45 songs on the Lego Rock Band disc. However, there are are hundreds of songs available to download, and it is compatible with a select amount of Rock Band DLC and exports.
Yes you can
Rock Band 2 doesn't start out with the same songs as the first game, but you can purchase some of the songs from the first game in the store, as well as new songs.
No. You can, however, put Rock Band 1 songs on Rock Band 2 for a $5 export fee. See below for a guide to importing/exporting different Rock Band games.
It should do it automatically if you have the songs purchased on the hard drive.