Though I don't use surface go, I used to have surface 3 before upgrading to the pro 6.
So I'll answer it based on my experience of surface 3.
The windows 10 works really well. You can use it as normal laptop, yes. You can either use external keyboard or buy the type cover (comes separately. Same goes with the pen)
I never had this problem.
It will be lagging. May not lag much if you use a smaller size of pen/brushes but it will start to lag once you use bigger brushes. Will also start to lag once there's quite a number of layers. This makes coloring... not a fun experience for me. But it was still bearable.
On another note, there's this video:
