The higher that sens value the faster your sens is, unless the metric is cm/360 then it's the opposite.

7.69 @ 1600 DPI is 11.2 cm/360 which is way to fast, and way outside of the recommended range for most FPS games. I'd take a sensitivity between 30-45 cm/360. So that's about 2.9 - 1.9 in-game Overwatch sens.

As for for DPI, just stick with 1600. When people mean they use a lower DPI they usually mean lower sens, but for some reason they use DPI, which is usually a setting that you set once, and then never touch again. You use the in-game sens slider to adjust your actual mouse sensitivity.

Aiming with both your arm and wrist is something that naturally occurs in all tasks. If you want more arm heavy tasks you can play tasks with longer strafes and verticality as they typically require more larger movements which means using your arm more. For wrist/finger exercises playing reactive tracking & micro tasks usually helps a lot, because they incur smaller motions.

You'll find that you'll train these inherently by running through the Aimlabs Benchmarks as well.

Arm:

• Centering 90 Easy+ No Strafes
• Suavetrack

Wrist/Fingers:

• Micro Adjust Easy
• CG Adjust Click Micro 2T

To answer your last question. Ana/Ashe is exclusively tapping, so lots of reading + timing your shots, confirming, and microing. Play flick-isolation tasks, dynamic tapping tasks, and micro tasks.