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In either case, I would enjoy some assistance on how to choose and what to do to benefit from siduction.
I really want to stay as close as possible to the any main distro, but I also really don't want to install bloat just to leave it aside. Maybe another distro is better for me, if so, which would be recommend?...
In 2008 I was exactly where you are -- sick and tired of MS putting their fingers into my system and into my wallet, and determined to make another OS work for me. I distro-hopped for 2 years, starting with Ubuntu, on to Fedora, e-live, Arch, Slax, Debian, etc. When I tried sidux, I found I was learning more about Debian than when I ran Debian stable, and I appreciated that the software packages were newer versions than stable used. So here I am still -- no need to try anything more.
My main hobby is genealogy, and because the best genealogy tools are designed for Windows, I need to run a Windows VM. (Tried dual booting -- no comparison to having your Linux system available while using the Windows VM). I also consulted for a number of years, up until last year, and that company required that I keep their data encrypted. So I built a 10 GB encrypted file and used Zulucrypt to access it. So my main productive siduction system is a little complex, with qemu/KVM and Zulucrypt along with other productivity software. A few years ago, I built a setup to convert all of my recorded music, from 78, 45, and 33.3 rpm records to digital. That was complicated, both hardware and software. My point is, siduction IS Debian and is fully capable to support all kinds of productive work.
However, sid sometimes gets a little broken, and you have to have that possibility in mind every time you run "apt full-upgrade". This forum has an Upgrade Warnings topic, and you need to check that if there is any doubt about packages to be upgraded. For example, in my case, I'm always alert for qemu, libvirt, KVM, libcrypt, and zulucrypt and nvidia upgrades, because if one of those comes in broken, I will have a non-functional system until I fix it.
Also, with other Linux distros you can usually set up their source repos and be done forever. That is not the case with siduction. You should set up the debian experimental repo, but leave it commented out until you need it. You also could find you need the debian stable repo at some time, for a particular package that is broken in sid. I have wire-desktop repo enabled because I use wire. So you will spend a little more time adjusting your repos with siduction that you did with Ubuntu.
On your second question, yes, some "fixed" packages will be automatically pulled in from the siduction unstable/fixes repo, but you also might need the siduction experimental repo. For that one you will use "apt install -t experimental packagename" to get a particular package.
I hope this helps build your confidence that siduction is a great choice for a linux enthusiast.