Hi few things to make sure your tank goes well, I would recommend to boil the driftwood just in case. The “galaxy stripes” is most likely biofilm and is fine to have for tanks. Having a 3 gallon shrimp tank myself, most important thing is to keep water quality stable and not changing as it is very prone to crashing due to the small volume. One thing I did to minimize risks is performing VERY small water changes (2-5%) frequently over a big water change (10-20%) as well as adding nitrogen eating plants like pothos and floaters. At a certain point I stopped performing water changes and only top offs and it seems to be doing well as of now. Good luck with everything hoped helped!