Back to the original topic:

I'll follow your advice, i. e.:

(1) I will create a second key for unlocking manually.
(2) I use the random key method for swap, now. I knew of this swap partition capability, but I only knew how to use it with swap being a regular partition. But I had no idea how to implement it in this scenario. Thanks for that!
(3) I intentioanlly created a swap LV on /dev/hdb, although I have a swap LV on /dev/hda, too. The computer is quite old and has not a lot of RAM, so it may need swap more often than newer hardware. The striping capability of swap can be quite useful, here. But maybe I find that I don't need it, then LVM will allow me resize everything.

Best regards!

gargmael