I used to run orb on veno because lol, but it's only 12 damage and 4% slow, for chasing I think it's good, but for lanning I think you should just put the money towards aquila.

For roaming I usually go PS, VG, VG, PW, VG, PN, VG and after that depends what we do.
I think it's essential to have 1 point in to PW and PS by level 7, and maxing VG gives you the most damage potential. VG deals 50% more DoT than PS, and has 100 strike damage, not to mention a much more potent slow.

At level 4 PS deals 300 damage + 14% slow vs VG at 550 damage with 50% slow.

4 PS might be good, but once you are out of the lanning phase, VG is superior, and personally I think veno is scary enough in lane regardless of 1 PS or 4 PS. You can easily just drop VG and chase people down before they can get to their tower, so harass through fear is more effective.

And obviously you need ward for chasing, block, vision, taking down towers, etc.