Plant babies! Now what?

We set up this little 20 gallon in October and did a complete revamp in January after having a cycle crash (changed from gravel to sand and removed all painted decor).

I just noticed this stem has roots growing, so what do I do now? Pin the stem down so the roots grow into the sand? Wait until the roots are longer then trim and plant?

While I have these photos posted, I’d also welcome any feedback on the tank - set up, chosen plants, what would improve it, what to get rid of, etc