My housemates rats always smelled sweetly of the aspen shaving bedding. He also kept their cage incredibly clean. It was actually a huge chinchilla cage, many levels for maximum space for them to run, play with toys, chill in hammocks, etc. Boy rats can have a little more of an odor, but they're also more chill than females. Keep their cage clean to eliminate most odor problems.
You cannot get just one rat. They are very social creatures, and do very poorly when kept alone. They play with each other, groom, snuggle, and basically spend all their time together. My housemate had three girls, and they were very spoiled, happy ratties.
No experience with ferrets. I am told the premade feeds contribute to their odor problem. Also that those feeds are terrible for them.
You see, ferrets, like cats, are obligate carnivores. They should have no grains in their diet, only meat. Manufactured dry foods need grain to act as a 'glue' in the feeds, so right off the bat, it is bad for them.
