Doesn’t completely answer your questions, but may quench some of your curiosity. This is copy and pasted from another of my posts. “Not sure what the hospital cap is for a lvl 1 hospital but at lvl 25 your hospital can hold 400k injured troops. Keep in mind that by building wards you can increase your total hospital cap.”
Just to build off what Tia said, you can also use research to boost your max Hospital Cap (it's at the bottom of City Growth).
Thanks guys! I know how to build my own hospital cap up! I was asking for the purpose of selecting targets for kills ! If anyone comes across the answer please share with me !