Why is it "women"?
Cause it's plural :o
So češi would be "czech men" then ?
Yes, but in this case (locative) it is o Češích.
Is the "ty" really necessary?
The meaning is a little shifted here. "Co víš o...?" is a regular question "What do you know about...?"
With the added "ty" it's usually (also depends on intonation) a rhetorical question, roughly meaning "You actually know nothing/little about..."
It's not. But it can be used for emphasis.