Help with Invoker?

Chaos Meteor after a Tornado/ Deafening Blast is good. Cold Snap and Forge Spirits is great for ganking because of the nearly permastun.

Also using Ice Wall and blinking behind them to use Deafening Blast to push them into your ice wall is super fun!

When pushing, Alacrity on your spirits can be useful for melting tower armor. If you have a necrobook lvl 3, always use it on the warrior. They fall soooo fast.

Why use a Sun Strike in team fights if you're going QW? It will do less damage than a Chaos Meteor. Also if you have ample time to practice try learning how to catch people with Ice Wall I don't know how to do it personally but I know it can be done. That might help secure ganks a lot more with the move slow. If not just plant it in their escape path, simple. Also try to use Forge Spirits they can really help with ganks by reducing armour.

Like Force Staff> Ice Wall?
or turn and catch them on the edge?

Both. I go Eul's + Ice Wall though as Euls on QE voker is legit.

TBH, I wouldn't get Force Staff. Go Euls if QE and Orchid of QW, then get a Blink Swagger. Since you're playing QW, the usual combos are:

Ice Wall + Cold Snap
Tornado + EMP (duh)
Ice Wall + EMP
Deafening Blast + your team
EMP + Cold Snap
Tornado/Euls + Ice Wall

Your endgame ultra-rampage getting combo is:

Tornado > EMP > Meatball > Deafening Blast > Refresher > Meatball > Blast
Then to pick off the survivors 1 by 1:

Blink Dagger > Ice Wall > Cold Snap
Euls + Sunstrike
Alacrity + Forged Spirits
Tornado + EMP

Orchid QW Invoker makes you a scary ganker with Cold Snap, Ghost Walk and Ice Wall. I cannot stress enough though, get a blink dagger and a sheepstick no matter what kind of Invoker you are. Also bear in mind that if you have Euls, you can escape by Eulsing yourself and blinking away as you come down. Ghost Walk is unreliable as dust makes it easy to kill you, especially if you have low Wex.

So...

For QW, I go Phase > Orchid > Agh's > Sheepstick > Refresher?

Does Ice Wall do DoT, like meatball? Because I was thinking Meatball > Cold snap for single targets.

Here are my choices of spells, see if you approve. These are for QW invoker.
So ganking would be: Ghost Walk > Orchid > EMP > Cold Snap.
Single target: Cold Snap/Ice wall > EMP
Early Teamfight: Tornado > EMP > Ice wall > Cold Snap
Late Teamfight: Tornado > EMP > Meatball > Deafening Blast > Ice wall/Cold Snap/Refresh.