But the cold hard truth is that as bad as it was to fully retire the iMac, getting rid of this laptop (which has the corpse of a previous laptop on it as well), is going to be really unpleasant and scary. So, in the spirit in which I do all this kind of work, I'm going to tackle the biggest bang for the buck first: the iTunes media.
(And I will acknowledge that yes, I've already excavated a huge amount of stuff to Google Drive and Flickr, and that was not a trivial exercise.)
First, I set up iTunes Match. So at least everything on the laptop already is now up in the Apple Cloud. That's nice. I even tested to make sure that an iDevice with absolutely nothing on it yet could then connect to all that goodness. Along the way, I hooked up a different iDevice (which had a somewhat populated music library) with Apple Remote.
Second, I wanted to get a sense of the scope of the problem. A replacement laptop is not going to have an optical drive, and R. gave my optical drive to his mother (with my permission). So if I'm going to get anything off a disk and onto my laptop, before retiring the laptop is better than after. I looked at the plastic bins of CDs in the basement, came up with a rough estimate of 500-1000 discs, of which at most about 200 have been ripped. Yikes.
Third, I pulled the external hard drive out of the hutch (the hutch of purgatory, where projects wait for Someday/Later). It is Large (500 Gig). I think it is Large Enough to rip all the CDs onto. I think.
Fourth, I checked just how big the iTunes library is on the laptop: about 147 Gig. Hmmm.
Fifth, I made sure that I had the correct settings already for moving an iTunes library. Yay! Happy dance!
Next step: plug in the external hard drive. Decide what to do (if anything) about what is already on it. [ETA: Delete all the backups since R. has set up a Time Capsule.]
Then: copy laptop iTunes library to hard drive. [ETA: Estimated Time 2 hours. Yikes.] [ETAYA: Closer to 1 hour 20 minutes. Yay!]
Then: point iTunes at hard drive; make sure everything made it. [ETA: Surface check looks great! The size of what is over there looks right. Not sure what level of detailed checking is justified; probably not a lot, given that I put everything up on the cloud anyway. Weird. This is going way more smoothly than I had anticipated. I'm quitting for now; I'll plug it back in tomorrow, make sure I didn't imagine all this, and see if I can rip CDs to it and have them migrate to the cloud and then reappear as downloadable in the other iTunes instance. If that works, I think I can probably nuke the iTunes instance on the laptop because it will be genuinely superfluous at that point.]
Then: start ripping the rest of the CDs (or at least those I don't just want to throw away immediately) in the plastic boxes to the external hard drive. I'm thinking 10 a day for a few months ought to get most of it.
With iTunes Match set up, in theory as I add stuff to iTunes, Match should sync it up to the cloud. Since it is all on a hard drive, I should be able to just plug it into a new laptop when I get it.
Assuming any room remains on the hard drive, I can just move over whatever I want to keep that still lives on the laptop (and the previous laptop's corpse) and I should be good. <-- This step is so vague it may qualify as underpants gnomes. [ETA: NOT underpants gnomes! R. says that he can dump what's backedup to the Time Capsule onto any new laptop I get, no probs, that's what it is for. Woot! Seriously, woo fucking hoo!]
ETA still more: As a side effect, I decided I should stop storing the hard drive in the box I got it in, but move it to the Amazon Basics zippered thingamajig I had bought a while back but never actually used for anything. It is now a Memory Binder: the thumb drives, SD cards and external hard drive all fit in there nicely, along with the cords for the hard drive.