Aspen is okay, but if it gets damp, they'll be damp, and they'll get infections. I only use newspaper with water snakes (and most others). Even then, I've had occasional problems with skin infections. A good basking light with a rock under it does seem to help- clean and bleach the rock regularly.
Another problem with aspen- most of the foods for Nerodia will get a lot of aspen stuck to them, so a greater risk of ingestion by the snake.
Water snakes are not aggressive, except towards their prey. Wild ones are often highly defensive- they will readily bite if handled. It has been my experience, though, that juvenile natricines almost never bite, but get more likely to with age. Many other snakes (Elaphe, Lampropeltis, etc.) seem to be the opposite- juveniles are much more skittish and prone to biting, but adults are more mellow. Either way, once used to people, they rarely bite. I've had both CB and WC specimens of several different species of Nerodia in the past, and all eventually calmed down nicely (except the WC N. taxispilota, but it was in bad shape and didn't live long enough to be considered a fair representation).
As for letting it go, it isn't just a question of whether you can 'handle it'. I'm sure you're capable of giving it adequate basic husbandry, if you put your mind to it. However, do you even know whether it is legal for you to keep it in your area, or to collect it from the wild? At the end of the day, it is a wild snake, and I think it belongs in the wild, unless there is some good specific reason to take it into captivity.
BTW, I currently have 9 Nerodia. I love them, and I use them a lot in educational programs. However, if I was just considering a pet, they'd be WAY down on my list of pet species.