Ok, my question are 1. i have a large collection of photo saved on an external drive. but the catalog was completed missed up. just bought a new iMac, my plan is to save all my photos into an external drive. i don't want to save photos to the new computer, because it will be filled up soon. So my plan is to transfer all of my photos into another external drive. what is the best way to handle this situation?
I'm not 100% sure I understand which of the several situations you are asking for help with.
If the catalog is messed up, do you plan to try to fix it, or do you plan to start a new catalog (and thus lose some or all of your work)?
But you can move photos from one disk to another, and you can instruct Lightroom to import photos to the external disk drive. Which specifically do you want to do?