I fortunately already have SuperDuper.
I found the following paragraph in the SuperDuper manual:
QUOTE FROM SUPERDUPER MANUAL:
"Don't use SuperDuper to copy a full boot image from a PowerPC Macintosh to an Intel Macintosh. The OS isn't universal, and thus won't work properly on a new Mac.
Instead, use the migration assistant that appears during the first boot of your new Macintosh to copy your files, settings, and applications from your old macintosh (or from your copy) to the new one"
So the bootabe image is just a safety copy, just in case the migration assistant messes up?
And I will find my catalogues and images on the new computer, I guess.
But for back-up, should I overwrite the external hard drive with a bootable copy of my new computer (after successful transfer), so everything matches?
I heard that there can be problems, especially if you still have PPC only software (which I do).
There can indeed be issues, but they are very rare. There are only a few things which do not run well under the Rosetta emulator provided with Intel Macs. Just this week I have successfully migrated a G5 iMac to an Intel iMac, and a G4 PowerBook to a Mac Mini. If you do have an app or two that are difficult, just delete them from your new Mac and re-install directly. That's certainly better than doing all your apps. Interestingly, in my experience it's not so much the transfer of apps that causes trouble, but rather all the files and personal settings. With apps you just pull out the discs or download and away you go - it takes time, but it's not hard. With personal settings, such as bookmarks, mail settings, backups etc., it's another issue entirely.
With regard to SuperDuper - yes, it does not always work to boot a PPC clone to an Intel Mac - but you can use that clone to run the migration should there be an issue with the HD in your old Mac: migration does not require the clone to be booted.