Kind of a Stupid Question (Regarding General Small and Furry)
 

Disclaimer: this is an entirely hypothetical situation. I just want to know what works and what doesn't.

I had a kind of ridiculous idea of keeping many different types of small critters in the same enclosure. The critters in question are: guinea/skinny pigs, mice, dwarf hamsters, hedgehogs, ferrets, and degus. Do any of these combinations work or not work? Is this a terrible idea?

Note: In this idea, space, food, other resources are not an issue. I'm just wondering about the compatibility of the different species.

ferrets eat mice so you shouldn't keep them with mice ,you really need to find out just what all these animals like to eat and if they can pass diseases onto one another. They could up making a meal out of one another .
I have a niece that had a rat and a bird , she let her bird out of it cage and it landed on the rat cage and the rat ate the bird . She didn't know rats ate birds. :(

Definitely the ferrets need their own space--as Barkingdog pointed out, they're predators and carnivores and will eat, at least, the mice and maybe even the guinea pigs, degus and hamsters.

I don't think I'd try to permanently house any of these species as mix-and-match. Even mice will kill each other if they're overcrowded and, unless you can find concrete research as to what constitutes 'overcrowding' for each species, it might be hard to tell which (if any) combination would work ahead of time. A degu might be perfectly comfortable with another degu in a large cage, but add, say, a hedgehog to the mix and all three animals could be stressed by having strangers in close proximity, even in a large cage. Even if they didn't openly attack each other, they might suffer long term health consequences from the ensuing stress...

If you do some homework and find out that a combination might work, make sure you make any introductions very slowly and cautiously. Just because a pairing might work for someone elsewhere, it doesn't mean that all individuals of the species involved are equally tolerant of each other.

But honestly, though I might allow them all (except maybe the ferrets) to mingle (supervised) in a large space (like a room) during the day, they'd all be sleeping in their own cages at night if they were mine...