Congrats on your purchase. The optic question is kind of a loaded one though, especially at such a low budget. I'd say spend the 150 on flip/back up irons, get good with them, and save for a better optic, that also fits your needs. For what it's worth my first AR came with a Bushnell TRS-25, which for a budget red-dot, is very decent, and holds it's zero. I think those tend to be around 90 bucks. If you want magnification, a bit more cash will get you a decent Nikon, or Vortex.
Just my opinion.