If you do an automatic install and select btrfs as the filesystem, it will automatically create the subvolumes you need for snapper and timeshift. That being said, you should only use one of those.
Unless are you are trying to support suspend to disk, you probably don’t need much swap. If you are going to use zram, I probably wouldn’t add any swap since you have 32GiB of RAM.
Just install gnome and add sway afterwards.
We have a profile and instructions for how to install it in our community repo.
You can use them if you want to. There are pros and cons. Personally, I would install everything from the AUR unless you have a compelling reason not to. I would be wary of unofficial flatpaks. I also see no good reason to install calibre as a flatpak.