Yes Lumia 950, 950XL support Continuum today. No, they aren't x64 phones and don't support x64 apps. They aren't restricted to the app store, you could sideload UWP apps if you had them. UWP apps these days are "full windows apps" for all intents and purposes these days. There may not be as many UWP apps right now as there are the long legacy of Win32 apps and the deep wells of Android and iOS apps, but there are some very good UWP apps out there, some of which are very useful in Continuum.