depends if you want to layer them all into one sound or use multiple.
You can use one hat or many, depending on the context you're looking for.
It's the same as layering any other element, you have to figure out how the layers fit together.--->one layer
other wise, it's the same way, but playing at different times.---->multiple layers with varying play
Look at the sound of a cymbal, and look at the sound of a drum machine cymbal....
Then decide how you want to layer them or play them..
edit: they don't have to sound different, but they can have characteristics that are different.
it really depends on what you want, and quite honestly this thread is so ambiguous that you probably won't get the answer you're looking for, unless you specify the problem a little better.
This is a question about YOUR TASTE, as a creator.
I know rusko has a phaser or a flanger on his hi hats, and some times he also pitched the shit out of them and made a cool little dittle with it.
Many producers don't even touch the damned things and they keep the beat like a real drummer would.
So you have to consider your context a little bit more and especially with the style or genre you're trying to do. Or, disregard all that shit and just make some crap and experiment to figure out what works for you and what you like.
TL;DR: doesn't matter how many hats you have, you can easily just put 0 as you can put a thousand..