Ferrets should have litter that does not clump and has minimal dust. Like I said, pine stive pellets work awesome and are crazy cheap. Actual litter that works great is yesterdays news or a similar product.
They usually have no issue being around cats. And if the cat has a good food and you want to feed kibble, there are many cat foods that are far superior to ferret foods. So you can even just leave one dish out for all.
Ferrets do not need to be outside. They should not ever be outside alone or without a harness. They will not survive and do not have a homing instinct. You can take them outside with a harness and its fun following them around. But be aware, its extremely rare that a ferret will follow you like a dog, or even cat while leashed.
A great forum for ferrets is The Holistic Ferret Forum
. Amazing people who are always willing to help out.
Oh, and you can keep a ferret alone no problem as long as they get out very often. They should have at least 4 hrs out of cage time a day.