1) Last time I tried it was reasonably fast for a dynamic language - somewhat slower than javascript (V8) but faster than python (cpython) to give you a ballpark

2) Yes, but ou will not use native widgets. The way you write applications is: you write code by modifying the behaviour of objects in the Pharo application (which is your editor, debugger, GUI, version control system and so on), then you strip off the parts you don't need (such as what you used to write the application in the first place). Hence you will probably use the default Pharo widget system (take a look at some Pharo screenshots to get an idea)

3) Last time I checked it was planned, but there was nothing yet