when shaggy said you can import most or RB1's set-list into RB2, he means all the set-list except for 3 songs (Paranoid cover, Enter Sandman, and Run to the Hills cover)
Run to the Hills has been rereleased with the master track.
The thing to do would Buy Rock Band 2's bundle, then buy a RB1 guitar seperate if you want to do the whole 4 man band thing.
Then rent Rock Band 1 you don't need to buy it to copy the songs just need to have the disc for a total of 5 minutes, cash in the 20 bonus songs for Rock Band 2, DL the 4 freebies, then you've practically doubled your song count for maybe 15 dollars (RB1 rental + the cost of downloading the import key from PSN/XBL)
then pick up RBTB