Hm, leveling order thoughts?
W is DPS and gets very good returns from leveling. I don't think you can ignore it, at latest second.
Q is his slow and secondary source of DPS since cooldown scales. Slow goes from annoying to deadly. Seems very useful as first or second level as well, but not sure if critical.
E is his mobility/burst and the difference between high level and low is night and day (24 to 12 second base cooldown, with max CDR leveling it means you can cast it several times per fight for chasing/escaping.) That's a great benefit, but the question is of opportunity cost - you can't not level W because his damage looks terrible without it, and Q helps him function as a tank/stick to things/poke.