Unsure if you'd get 3 monitors working, I know 1 will. All depends what you do on your phone.
Dex mode works fine if you do things with microsoft office or web browsing. If you use real programs then you'll hit a roadblock. Phone apps work fine too, they just might not be optimised for desktop
Eg, browsing the web, writing word documents, PowerPoint. Those all work well, basically chromebook things.
Oh and a mouse and keyboard should work too
