If I install a new ROM does that erase all my installed apps and dat?
Unless you wipe all your data before the update, you do not need to Reinstall applications or Restore application data. But when flashing a completely different new ROM, it's recommended to do a full wipe before proceed. Further more, If you are planing to do a full wipe you can use a application like My Backup Pro or Titanium Backup to back up all your applications and data.