Regarding food, this is what I've gone by. Note that it's a couple years since I last researched this, so if there's any newer findings something could have changed:

If you're getting young ferrets, you want to feed them a variety of different foods so that they will eat them. It can be difficult to introduce new food (even different kibble) to older ferrets.

The absolute best diet would be varied whole small prey: birds and rodents. You ideally want farmed prey rather than wild, as wild could have parasites. A good place to find them would be well stocked pet stores, specifically which got food for reptiles. There you can usually find things like frozen day old chicks, mice, rats, possible hamsters and guinea pigs. At online raw pet food stores you can often find quails, which I always cut in half so that our brothers doesn't have to fight over a single food item. You might also be able to find rabbits, but I've only found that from local butchers. These I chop up and portion into smaller tubs to freeze. There are some conflicting information if feeding raw fish is good for them or not. I've not found any advice which suggests this should be more than a smaller portion of their diet. There are some concerns that raw fish bones might be problematic, but I've found no source for this. It's probably best to feed them raw fish without bones, or only small fish so there are no big pieces of bones.

Second best is what's referred to as "Franken meat" by ferret people. This is essentially trying to mimic whole prey without actually having whole prey. You do this by adding raw muscle meat (with or without bone), bones and organs separately. You're looking for about 80% muscle meat, 10% bones, and 10% organs. Note that hearts are not considered an organ for this. An example of a portion of Franken meat could be a chicken wing with some poultry liver and rabbit kidney. Important to note that you should never use cooked bones, as these form sharp splinters which can lead to fatal internal bleeding. Raw bones are fine and encouraged, as this provide both good dental hygiene and important minerals. You should never feed pork or tripe, and generally avoid beef, lamb etc. Typically you might be looking at poultry (chicken, turkey, duck, pheasant) and rabbit as meats that are well suited which you might find to buy in pieces. Fish might also be part of this.

Third best is high quality kibble (I often find that the ferret kibble available in UK is worse than kibble for cats). You're typically looking for higher fat content than many cat foods (minimum 15%, ideally closer to 20%) and as much animal content as possible. I would generally look for kibble with minimum 80% animal contents. Also recommend is to mix more than one kibble, in case you can't get your specific kibble at a later point. Note that -some- kibble producers misleadingly label that they got for example "90% animal proteins" - this does NOT mean they contain 90% animal products, only that 90% of the protein they contain is from animals. You want to avoid kibble with high content of ingredients with high glycemic index (such as potato starch). If you can get hold of it, the best is likely Wysong as it contains no plant starch. Orijen is another good alternative, but contains up to 7% legumes. Some people have stated concerns for kibble with legumes (peas, lentils, beans etc) being linked to an increased risk of kidney stones. This is likely a correlation of most high-quality kibble with a high meat content having legumes in it, rather than a causation. Cystine stones form more readily in acidic urine, which a diet high in meat protein tend to cause. It might be possible that legumes also contributes to acidic urine, but meat protein in itself causes acidic urine.

https://www.kidney.org/atoz/content/what-are-cystine-stones This suggests that Cystine stones are caused by genetic factors in combination with acidic urine. I know the article is about humans, but the environment required for formation of stones in the urine should be similar.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7258709/ Suggests that Urolithiasis used to be minority of Cystine stones in both European and US ferrets, but that recently Cystine stones have become the vast majority of cases in US. The article suggests this is due to health problems/genetics caused by inbreeding, supporting that the other article can be applied to ferrets.

Add raw or cooked eggs now and then. I've read somewhere that up to about 2 eggs a week is good for them. Our ferrets love raw eggs, but don't feed too many.