Greetings

Can you tell I don't do this very often? (Its been some number of
years and I'm not remembering most of the details and I just don't
like oopses!!)

One of the things that I'm doing different in my new install is that
the system itself is going to be on a raid-1 (mirror).
So how can I start by setting up the mirrors?
(4 drives - - - 2 mirrors)

Then - - - I've got a lot of software that I have installed on my present box.
How do I generate a list of stuff, easily human readable, so that I
can set up the new box with most of the stuff that I have on the
present system?
(I am moving from debian testing to devuan testing as well if that
presents any gotchas.)

I have used partitions for /efi, /boot, /, /usr, /usr/local, /var and
/home for a long time now.
Any need to change this practice?

Had used btrfs for my latest filesystem instead of ext4 upon
recommendation by a mentor (who is now deceased).
Is this a good idea or are other options 'better'?

Hopefully not too many questions!

TIA