Wanting to main Vayne

Just watch gosu and copy him

Right now probably Shiv->IE->pd than more situational stuff (e.g. LDR/Merc/BT/GA/Bork/BV) is probably the best build for the spicy Q crits, not to mention far less demanding mechanically compared to an AS style vayne.

I also probably wouldn't recommend maining vayne unless you've got gold+ decision making and the game knowledge to go with it. Easy to watch fancy montages of vayne 1v5s, but vayne is one of those champions that if you make a poor decision, you'll probably die instantly and be more or less useless. This is true regardless of if you're a mechanical god or a more typical player, as mechanic don't help when you're dead.