Hey . I can only answer some of the questions. Hope it helps tho . It its possible to train an older ferret . I used to have 7 and we rescued them all most where around the ages of 3 and it worked perfectly . Mostly just found there fav vorner to go in and put the box there and it worked . Caging is pretty simple and wire cage will do really . Im sure you know this but anything they can fit there head threw there body can go threw as well . Most that I have got lonely very easily . They love to have another ferret to snuggle up to . Well at least some . lol .
Hope it helped a little bit
~Steph~