Carpet pythons are a great snake to own, don't get unmanageable but still get a nice decent size
Depending on the locality most carpets will need far more than a 3 foot viv, minimum really would need to be 4x2x2 (some larger specimens can reach 8foot!!) Jungle carpets tend to be around the 5-6 foot but some have exceeded 6-7. A 3x2x2 or better 3x3x2 (a bit more height) will be fine for a small-medium specimen.