Some questions about Micromanagement of military units

So I have some difficulties with micro:

1. With skirmishers, when I hit and run, a lot of shots are "wasted". For example, I have an army of 50 skirms, I right click a musketeer, and even though only 10 shots are needed to kill the musket, all 50 hit that single target, wasting 40 shots. I find often this is less effective than just not microing at all.

2. When I use cav, if I have a large army(ie 40 cav), if I just right click a unit, they all get stuck on each other trying to target that unit. I usually just struggle to select 3 horses at a time but my APM is low.

Is there a way I can just say "attack anything in this area"? like a hotkey or something. I often have fights where I have the superior numbers, but I lose because my micro is bad.

3.Is there a way or hotkey I can command a formation not to wait for the slowest unit? Often I'll have 20 horses, one will get snared by a pikeman, so now I'm struggling to find the one that's snared to run them into the enemy, and select the rest to run away.