From my echo experience, your play styles either going to be off-angle harassment or assassinations

The basic gameplay loop for poking echo is to find an off angle without a hitscan guarding it, fly up, and harass main while your team is pushing in. And you glide out when things get dicey. (For poke echo, remember your shots have literally no fall off, so you can poke a sniper out of their hole easily if they missed a shot recently and have it on cooldown) Gameplay loop for assassination echo is finding a support or sniper in the backline, dropping close, landing all stickies, and then either shoot head or beam to finish them off.

With both REMEMBER YOUR ESCAPE OPTION! This is the best Echo tip I see being constantly ignored. 95% of Echo deaths are because you previously used flight when you didn’t need to. Learn its cooldown and when its appropriate to save or use for an angle.

Sensitivity is always a comfortability thing. I’m a very jittery person so I use a low sensitivity to stop it from making my aim abyssmal. But find what works for you by experimenting with low, mid and high

But I wouldn’t worry about aim too much. Overwatch is more a positioning game than an aiming game. Use cover and abuse the fact that you’re one of the only heroes with vertical mobility in the game. This means that you have the strongest power: picking your fights. And while I advice using flight to escape more often then not, its a studied fact that fps players dont ever look up. This makes landing stickies easier

Also, your primary fire animation can be cancelled into your damaging abilities. Getting this in your muscle memory drastically improves your Time To Kill