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?