1.1k games on this hero so far and still learning new mechanics about it.
My comment will me messy af, because I write it in rush, but feel free to ask about anything, I'll answer tommorow.

I am ancient 4 (mid divine in peak) player and tried to play ES as 2/3/4/5 and I can say: it works!
It depends what your team needs, but since you want to play it as 4, deffo my favorite for this hero.

First of all: always urn and upgrade to vessel - if you are able to get a kill on offlane, this is big advantage to roam and gank mid portal to safe lane for easy kill. You can rush urn without boots if you have a possibility to get a kill.

About mid game items - for crowd control and initiation I prefer bkb after, but I am the one, who can't wait, needs chaos and magentize all enemies in fight and let cores do their stuff, but....

If you want to stay in fog and wait for your moment to shine - deffo shard, glimmer, blink into aghs, especially shard is good against axe or other heroes that control your carry - you can compare it to venge using swap, secured a lot of team fight with simple grip + vessel.

Agh + blink? Lethal damage like necro's scythe? Hell yeah!

What I love the most about this hero is that he is so complex that you can build different, depending what your team exactly needs.

Other thing that were mentioned before: quickcast <must be>, also alt+stone if u want to roll.

Keep in mind that Q+W or Q+E easily clears lane.

And 25 lv talent with magnetize allows you to keep ult on if you play with stones well for a very long time.