Need some help with N'aix

I've been playing a decent amount of games with N'aix recently and it's a hero that I never really touched back in DotA so I'm a little confused on his details.

Generally, I'm not entirely sure on how to build him, how to use Infest correctly and what heroes he works well with.

I've been skilling him maxing Feast first, 1 point in Open Wounds early on (level 1/2/3 depending on the situation) then maxing Rage with Infest whenever I can get it.

Item build I'm generally going for Power Treads, Magic Wand, Armlet and Medallion and then it depends on the situation but I find myself going for Cuirass, BKB or Satanic depending on the situation.

Anyway, I'd like any type of advice you could lend on N'aix.

PS: AM pickers always underestimate the N'aix.