I think you know the pros, here are some cons...
Ferrets are really expensive pets. They very much are "balls of trouble" and their troublemaking can lead to really expensive vet bills. Their natural curiosity convinces them to search out items that are prone to being stuck in their digestive tract and eat them, to climb to great heights and then fall, take rides in the dishwasher and front loading washing machines, to find their way into the walls and behind the stove so that you have to pull out appliances and rip open walls. They are a huge pain in the neck. On top of explorational casualties, you have adrenal disease where you need to get $100 shots or $1000 surgery, and insulinoma where you need to give them daily doses of steroid so they don't have seizures and die. This isn't cheap either. Adrenal hits about 50% of ferrets and can show up as early as 2 years old.
The mess. Ferrets do have their musk odor as you know, and to keep this in check, you need to religiously dump their litterboxes and change their bedding as the musk is in their skin oils and builds up on their hammocks. Most ferrets don't potty train to litter boxes the way cats do. They poop where they want to and it's up to you to put down a litter box there. This goes for out-time too. Ferrets clear kibble from bowl to litter box in 3-4 hours, so you can expect at least one deposit from each ferret to occur during run around time i.e. in a convenient corner throughout the house. If you have carpeting in the house, you will probably be scrubbing ferret poo out of the carpet pretty frequently and it is very gooshy and soaks right in. Even if you put out litterboxes, you aren't going to catch all of them.
Destructive behavior. Ferrets get into lots of stuff and tend to knock things off of shelves. They climb rather well and find their way onto most pieces of furniture. They are very determined and have nothing better to do than go places they aren't supposed to be. Any place the ferret is going to be let out in has to be cleared of anything dangerous, poisonous or breakable doorknobs down. You also have to block off access to behind appliances and under furniture where they could get stuck. The other house members may object to foam spray-ing the stove and refrigerator to the floor or chicken wiring the bottoms of furniture in the living room. Ferrets dig up under mattresses and love digging holes in the couch to get under to where the springs are. That becomes a prime hiding place for toys and a great napping location. Restricting a ferret's out time to a single room is dependent on your ability to keep the ferret in. They are sly devils and try to sneak out at any opportunity. Once they realize the door goes somewhere, they may take to obsessively digging right at the bottom of the door. This will soon shred any carpet and can even damage a wood floor over time. Many ferrets are also toe biters and will nip at bare feet. If you are planning on satisfying their exercise need by letting them roam your bedroom at night, you might be in for frequent rude awakenings.
Don't get me wrong, ferrets are a great pet. Just make sure you and your family are ready for the bad parts along with the good. I'm just out of college and I have a permanent foster rather than an adopted weasel. I have a full time job, but I can't always summon hundreds of dollars at a drop of a hat to fix my weasel, so I have an older ferret that is a biter. Nobody would adopt her so she was pretty much fated to live out her days at the shelter. As a foster, I can go to the shelter for help with her bills if I need to. So many ferrets get abandoned when they get too expensive. If you're going to adopt, please make sure you can afford to finish what you start.
P.S. If you are anywhere near Maryland, I know a great shelter that needs permanent foster homes.
www.rockysferrets.com