Migration Assistant vs Carbon Copy Cloner

Is there a clearly defined "How To Manual" ...

Yes. The new Mac will ask if you want to transfer information from another Mac or a Time Machine backup. Choose the latter. You can probably choose the CCC backup in the same manner. I don't use it but it should do the same thing.

It takes a while to transfer data, not so much due to the connection speed but all the "overhead" involved with exhaustively examining each of the potentially of thousands of little files that have to be moved, converted, verified, etc. It's almost certain to take hours, but that's the best way to do it.

Set up your Mac - Apple Support explains what to expect.

I can't speak for Carbon Copy Cloner at all. But you can pick and choose what you want to migrate via Migration Assistant. You can do "everything" or just certain "user accounts". Here is the Apple Support article: Move your content to a new Mac - Apple Support

If you were happy with the performance, configuration, and behaviour of the old computer, then you can migrate everything. If you had a mess, then you might want to limit the migration to just your user account. You will have to reinstall any apps.

To expand upon @etresoft's reply:

If you were having software/settings problems with the old iMac, then depending on what those issues were I would not even migrate just the user account(s) as it may still bring over some items from outside the user account (at least it did so for me years ago with Yosemite's Setup Assistant). I ended up just manually copying my data and specific settings/preferences to the new system after performing a clean install. You could use CCC to do manually copy specific items as well since CCC has an option to select/deselect various folders/items.