You can have both WindowBlinds and Curtains installed at the same time, but as you might guess you can only have one theme from either of them applied at one time. I did read in another post that there was some small advantage to having WB installed (with its process running i.e. in Task Manager) even if you're using Curtains, so I'd leave WB installed if you already have it even if you lean more towards Curtains.
WindowBlinds skins more thoroughly that Curtains. That may be why some of your programs accept Curtains more readily that WindowBlind, Curtains isn't trying to change as much.
Creating a skin, Curtains starts with the default Win10, so if you just want to create a new skin with a different taskbar for example, you can do that, and everything else with continue to look like Win10.
There aren't a lot of Curtains skins out there yet, but it hasn't been out very long at all. Considering how new it is, there are really quite a lot. Probably because it is much less complicated to skin.