Cool side still too cold. Do I also need to weakly heat it?

[200xth]

Regarding substrate, I'm torn because it seems like there's no agreement on what is safe to use.

There's tons of safe things to use. Aspen, pine, paper towels, kraft paper, coco fiber, old newspapers...some people have biological substrates. You can use all sorts of things.

I wouldn't get too hung up on some of these things. You'll probably end up trying multiple substrates as time goes on, anyways.

As far as the temps, I agree with what MarkS said. Those temps are fine. FWIW, my cool side temps are always down around 72 (sometimes a degree or two colder).