The more space you give them the better the sizes you quote wont be anywhere near big enough , think 6x6x6 , they need cleaning out daily so you will have to handle them daily & feeding daily, if you cant afford the time i wouldnt bother personally , there not going to appreciate being shut in a tiny hutch
The walks with the dogs ok once the dogs ferret bomb proof , ferrets are not the sort off animals you can just get out when you feel like it, there fairly high maintanence