Blade Ambusher Merc - What are the important skills/links/affixes?

Hello, I want to set up an additional merc for uber bossing, and have read Blade Ambusher is the best (or one of the best) bossers. However, I am unclear as to what the key components to make it work well are. I am planning on using my existing Flame Link/life stack setup.

Skills - What are the key skills for bossing dps? Spectral Helix + spectral throw?

Support links - I have heard slower projectiles is important on the dps skills?

Item affixes - I have heard something about +1 traps thrown on belt mod, but I have not seen this affix this league.

I really feedback or pointing me in the right direction.

Thanks!!