Applications
Can you use the ones you want?
Some applications rely heavily on the window manager to handle their windows. When you choose a window manager, you need to consider whether your applications can handle your whole workflow. GIMP is an example that can cause problems when you use the tools in an undocked mode. With GIMP, you have an option to have all tools inside the application, called single-window mode. When running office packages, they usually do fine unless they are made especially for the environment.
KDE has many projects that need the desktop environment to operate. Watch out for programs that are spelled with a ‘K’ for no apparent reason. They are usually made for KDE. That said, most of them work across platforms, so don’t switch until you know you have to.
You may also notice that the whole tiling windows thing doesn’t suit you very well. If that is the case, don’t consider Awesome, Regolith or the do-it-yourself Suckless dwm. They can do floating windows, but not very well. Dwm can handle most situations, but you may have problems with application size exceeding the screen in a dual-head setup.
The same happens in Awesome if you have different resolutions on the second screen. This is not a big problem for most applications. It is worth it if you feel you can save on memory usage.
The thing to consider is if you want the notifications that come with the big three. You can take them with you, with some tweaks.