Hey beautiful work! That was a good idea using oil pastels along with acrylics! This way, you can easily paint over in layers and add anything later if you feel like it. I'm gonna try that sometime :) Painting the night sky is really fun and the paintings always look beautiful. Here's one I made- I made it on white paper but I'm gonna try using black paper sometime 🙂

https://steemit.com/art/@ashfreqk/stellar-love-a-watercolour-painting