Is the adventofcode.com fun/educational/worthwhile? I see it starts again Dec 1. I like doing things like this but end up regretting it as it sucks too much time solving unnecessary problems.
Obviously looking at resources to learn approaches to solving the problem isn't cheating, but there is some value in spending time just trying to figure out an approach before doing that.
For me, the answer to all three questions is - yes.
It depends on your previous knowledge, so some problems might seem too easy and/or some other problems might be too hard.
If you are an experienced programmer, maybe use AoC to learn/practice some language you didn't use before?