I think I can answer:
> So apparently anything made before 1923 will go into Public Domain on January 1 (which was yesterday at my time of writing), so does that mean I can just record a song from the 1910’s or something and add it to my game?
Close; any sound recording made before 1923 went into the public domain yesterday. The underlying compositions prior to 1923 were already public domain and have been for many decades. So that means, making covers of 1910's songs won't count, but using recordings that were made in the 1910's definitely do!
> Can I get a painting from the 1910’s and turn them into sprites?
You're allowed to do that, but in order to be eligible for the contest it must be from 1926 if it's not a sound recording.
> do I have to make something based OFF OF them and not directly copy them?
Either/or. You can make something based off of paintings from 1926 or directly copy them.