Depends on for what purpose you use it for and how good you are with improvising string/cord from. I'm only good with making relative short string with stingy nettles. As a matter of fact i just got home from making some of them. Some roots and vines are ofcorse cord, ready to use. Improvising however does takes time.

Paracord is great stuff, the cord is know for it's multipurpose uses. Multi-purpose things are usually usuable for more than one thing, but not a first choice for anything.
You could consider replacing paracord, with some strong cord, roll of twine and some sewning thread. This will not take much more space, but will give you the right sting for pretty much every job you replace with the paracord.

Twine is biodegrable. A nice feature if you builing a natural shelter. It's cheap, compact and easily carried. I use this stuff for loads of things, if i don't have the time to find/make some.
A little bobbing of sewning thread, for obvious uses and flossing.
The strong cord for lifting things and making strong connections.

The snare wire, is great because it's usually metal. So heatproof and stuff. If you haven't snared before, you probably won;t catch anything with it. Beter to call it just brass/steel wire.

The amount of string is usually as many as you want to carry. To little and you won't have enough and to much means you carry to many things on you back. It really depends on how you use it. Some people complain about never having enough and others never run out. Really the amount is a personal choice, i can't tell you how much is ideal. Just carry as much you thing you need and maybe a little extra.