So my question is can this work beacuse people have 3 hex alwes wisible around them?
Yes, you are always visible at 3 hex range, but it says in sneak mode, nothing about being unseen.
melee + PVP isn't recommended
I'm a newbie so I can't rightfully say, but with 200 sneak aren't you practically invisible at all times?
Nope, its maybe enough to fool most mobs, but for players with some perception you clearly need sneak 300% to be invisible. Then it depends on their perception. And yes again, they always see you at the range of 3 hexes.