Re: "the system has a more modern and 'flatter' look"
When it comes to Multi-monitors, workspace per screen is the only way to go IMO.
Few Desktops have Windowmanagers that do it.
Gnomes workspaces on only once screen default option isn't too bad - a little limited, but you can leave an app on another screen undisturbed while you flip workspaces on the main screen.
Openbox has a patched version that does workspace per screen (works ok with LXTQ, not tried with KDE/Openbox).
Enlightenment does it
But yes, the most functional are mostly the Tiling Window Managers.