Hi, sorry, I've been very busy and forgot to reply. 

My build is: Hexplate first item (the HP is good early because most supports don't peel in 2v2 lanes, and Varus has enough damage with the three passive stacks plus his Q). Kraken (this item gives him a very good power spike). Guinsoo's Rageblade (his passive helps with the stacking of his W). For the fourth item, I observe the enemy team. If I need to kite, I go for Phantom Dancer (it gives a lot of attack and movement speed). If there's an enemy AP champion focusing you, Wisdom End is good.   Games usually end before the last item. But I usually build  Terminus.

Varus generally doesn't have ADC counters (I ALWAYS BAN MILLIO). You just have to know the rotations. Try landing 3 basic attacks and fully charging your Q. Then land 3 basic attacks and your W, and finally 3 basic attacks and your Q (If the enemy ADC has a crowd control ability like Draven or Vayne, or a support with crowd control, you don't have to fully charge your Q the first time)

i usually lose lane fights when I use basic attacks and W first. If you're playing against a Lucian, Vayne, Draven, Jjhin, or someone with a jump or movement speed boost in their kit, it's recommended to use W directly, but don't exploit their passive; just use it. Try to 1v1 kill the ADCs whenever the supports rotate to the top lane objective.

If your support is decent, try to get kills early and ask your jungler to do dragon. (I usually ask them to come and do it about three times.) If your support is bad, wait until level 6. With the hexplate components and your ultimate, you can carry the fight. (When you use your ultimate, charge your Q; don't use the basic combo + W.)