Q:
What level would i attain if...............
A:
10 levels per 400 craft. So he would be 12 or maybe 13 if you were close to level 3.
As Terra said and assuming your crafting is level 1 when you start you will gain pretty much exactly 10 levels for taking a craft from 1 to 400.
It also does not matter if you are level 2 or level 70. You will gain 10 levels regardless of level.