WEll, you might be asking. Why Dark Harvest, is it better then electrocute? Well, i think so.. I played a few games with it, and it felt really strong. That E burst is really noticable. Especially with powerspike.

Dark harvest scales really well with E. Only annoying thing in early is, managing to gank within 30 sec of last camp killed. Cuz of E we are taking sudden impact too. Eyeball colector is just best of the 3. I like to take Ingenious hunter for zhonyas and protobelt CDR but this is up to you, and your preferences. Secondary tree, iam taking precision for early lvl up mana and execution damage.

Taking Q first is just normal. Taking E/W on lvl 2 depends on which side am i starting. If i start on red i take lvl 2 W, because i go for raptors. If i start blue i take lvl 2 E and go for wolves.

Starting items
Hunter's talisman for mana regen is best choice and refillable for gold saving later.

First back
I back after full clear + 1 gank. Best smite choice is blue one. And boots if you have enough for it.

Later
First completed item should be runic echoes with sorc boots. It will help with bursting, and it just feels good and right.
Definitely build lich bane, before protobelt, it will give you much more power.
After lich bane and protobelt Void Staff is complete must have. Without void staff, your damage is completelely screwed.
Next is choice between cap and zhonya's. Well, it really depends on enemy team comp. If you have to burst something down and they don't have much to stop you, cap is the choice, but zhonya's are really good, it just works well with Ekko, and his W > R combo.

I will just quickly explain how routes work. Always start where botlane will pull you.

If you start red: Red (Max W) Raptors > Wolves > Blue > Gank > Gromp > Back

If you start Blue: Blue (Max E) Gromp > Wolves > Red > * Gank Bot > Krugs > Raptors > Back
* Gank Mid > Raptors > Krugs > Back

Don't forget to clear at least one side of the jungle between each back > gank.