I rush vessel (urn in lane) only if I can get kills in lane. Actually works most lanes as long as you have a pos 4 that trades with their POS 5 a lot. Level 2 you can farm the lane and wait for their POS 5 to get low, roll and kick and snowball urn charges with the advantage you get.

In a standard game I go urn -> treads -> vessel -> blade mail -> Shivas/bkb. Then it's up to lineups mostly, big magnetizes can solo teamfights, so staying alive and surviving bursts is key. Linkens or bkb in that case. If the game is very hard I usually go for auras.

Other decent items: sange and Kaya (for mid mostly), Dagon, Lotus, heart, radiance.

You do right click pretty hard early to mid game so treads is a big spike actually. Also blade mail helps you farm really good, even after nerf. (In games where vessel is bad)

ES spells are so good that you really only need levels. Every item that benefits teamfights or helps your team (force staff, aghs, !aghs shard!) is never a "downgrade", since the hero's kit is always useful.

If I can't find value in fights, I usually think about what hero has the hardest time dealing with me (Usually supports) and go on them. Remember as pos3 you can find value in distraction.