IMHO it is at first much more important that the distribution is running well, is safe, and gets the required support so that it can establish itself among the many distros and remains for many many years an entirely European distro! I do not care in the beginning if it is called Donald Duck OS, mc2 Linux or whatever.

I do not have a Slimbook but they look really nice on their webpage. However, I miss the possibility to choose among hardware components like with Tuxedo Computers, which is also located in Europe.

Give it a try. Perhaps they may give you at least a hint.

Pcmanfm? Nemo? However, if one does not need a GUI I would suggest ranger, nnn or alike.

Oh, I did not know about the possibility of replacing xfwm4 with i3. I too am using i3 for some years and like a lot to have a clean surface which facilitates focussing on my tasks. However, never thought about integrating it in a DE.

You mean switching between the DE xfce and the WM i3wm, right? Yep, this works and it can indeed make life sometimes easier to have a DE and a WM aside each other.

I am absolutely with you about i3. Simply great (there is also dwm or qtile)! But it is a WM, not a DE, what OP asked about.

Did you contact TUXEDO Support Centre?