Kibble: Ferrets are obligate carnivores. A fully raw diet free of fruits/veggies/grains is absolutely what is best for them no questions asked. That said, you have to take extreme care to research this way of feeding to ensure that the diet is properly balanced. If it is feasible for you to follow this diet, that is best. Raw diet can be done on your own, and can also be found in the form of premade grinds.
Secondly, options like freeze dried raw (FDR) are fantastic. When fed alone, you need to take care to rotate the proteins you feed. It'd be best to mix 2-3 different proteins together each feed to ensure they're getting enough variety. FDR options are well-balanced in terms of meat, organ, and bone. I personally use Stella and Chewy's duck duck goose at the moment, but have used rabbit and chicken as well. I use FDR to replace 2 meals a day for my 2 ferrets. Each ferret eats about 6 pieces, so I feed 12 total each meal. $40 bag lasts me about 2.5 weeks. Another fantastic FDR (technically air-dried raw) is Ziwipeak, but that one can be harder to find--for those in the US it's currently available on Amazon.
Kibble is by far the most popular option, as it's what is most convenient. There are few kibbles available that are truly appropriate for ferrets, as well as others that are out there but not always easy to find. Wysong Digestive Support is the best bet as the #1 kibble. However when kibble feeding, you always need to mix 2-3 kibbles in case of product changes, discontinuations, etc. as ferrets can be VERY VERY picky about trying out new foods. So some next best options are:
Biting: Your ferret is most likely not being a jerk on purpose, and may be biting because: 1) They want to play 2) They want your attention 3) "Put me down/don't touch me please" 4) "I am scared/in pain" 5) "This is MY toy!" 6) Deaf ferrets can be more difficult, so more patience & understanding is needed
Ferret skin is thicker than people's so kits or unsocialized ferrets need to understand to be gentle. You need to communicate with them, not punish them, to train properly. 1) Build trust. Let them approach you while you're sitting down. Let them sniff you and handle them with care. 2) Yelp/squeal after a rough bite and walk away and ignore them for a minute or two 3) Put a drop of salmon oil on your arm so they know you are for licks, not biting 4) A "sin bin" (carrier NOT used for vet visits) can be used, but you must catch them EVERY time or it is ineffective. Put them in the carrier for 1-2 minutes. Any longer is unnecessary and they'll have forgotten why they're in there. 5) Redirect the bite by putting a toy in between you and the ferret 6) Say NO!! and use a hand sign (especially helpful with deaf ferrets) 7) As a LAST RESORT you can scruff if they won't let go, but not as a part of regular training (it can make things worse)
Trying to pull away from a bite can make them bite down harder. You can push in a tiny bit, just behind the canines, to help them release. This is not the same as putting your finger down their throat!!
DO NOT FLICK A FERRET'S NOSE. DO NOT USE BITTER APPLE SPRAY. (Kills appetite, harmful ingredients, risks associating food with the awful taste) DO NOT BITE THEM BACK. DO NOT PUT FINGERS DOWN THEIR THROATS. DO NOT USE HOT SAUCE OR CAYENNE PEPPER.
Corner Litter Boxes: These are actually generally ineffective. Many ferrets will not use them because they cannot fit their whole body inside the box. You should aim to have a box large enough that their whole body can comfortably fit inside. Options for this include the Marshalls' high back litter boxes, puppygohere boxes, etc. or a cat litter pan that you cut a low lip out of and sand down yourself. Litter boxes can be zip tied, clamped, or clipped to the cage to prevent movement.
In the litter box you want to use something like a paper pellet or pine pellet (a little harder to find) bedding. Stay completely away from things like Carefresh, traditional cat litter, etc. as these types of beddings can create a host of issues such as blockages, respiratory issues, etc.
Another option is puppy pads. I don't personally recommend disposable ones, as many ferrets like to dig and tear them apart and the cotton or plastic could be ingested. Not to mention it just makes a mess. There are reusable puppy pads available on Amazon.
For cleaning messes, if you let the poop dry some it is easy to pick off with a baby wipe (should just pick right up no problem). Spot clean using vinegar. It's simple, effective, and safe.
Messes: Ferrets are terrors. haha. The best thing you can do is try to adjust for and expect these messes. Using metal bowls that attach to the side of the cage is a good place to start. You can move the water up high to deter water digging (so they have to stand on their back legs to get water). For food, the metal bowls work as well or you can do a heavy ceramic bowl. Whatever you use, make sure it is not rubberized and doesn't have rubber non-skid feet on it. Ferrets are notorious for chewing rubber. I have these bowls, they're pretty cool. I also have a couple I found at petsmart in the small animal section. Just plain white heavy ceramic.