[AmityvilleHams]

For the short answer: No, just no.

Humid environments are very dangerous for hamsters. Their environment, if too humid, can lead to things like mold & general fungal growth along with respiratory health issues.

Soil isn't safe for hamsters. The most similar thing you'll find is pure coconut fiber and even that needs to be used very carefully to not be too dry or too moist(again, respiratory issues etc). Moss is something I would strongly discourage the use of - it inevitably traps humidity which you absolutely do not want in a hamster enclosure.

Live plants should not be used in the cage and potted ones outside the cage can be unsafe due to the soil. Hay can be very sharp and cause eye injuries and such, as well as being potentially dusty and a good way to introduce unwanted pests into your enclosure so it does require strict precautions like freezing at least 2 days before using it along with going through every piece to make sure nothing is too sharp etc.

Very deep substrate honestly does the job good enough in a very large enclosure and if you're using a safe substrate that is appropriate for burrowing it'll be much safer and still allow hamsters to exhibit natural behaviors.