If you want black sand, look at Black Beauty blasting sand. It's very cheap at Tractor Supply. As long as you aren't planning on Cories. The edges are a bit rough. It looks nice.
Live Plants don't have to cost a fortune. If you tie or glue Java Ferns to rocks or wood, they are easy.
As far as stocking ? Do your research.
Personally I would never mix an Oscar with Angels. He'd grow up and beat them up IMHO. An Oscar will eat any fish that fits in his mouth. They are very messy and will destroy plants and like to dig up the substrate. But they do have personality.
So if you want Angels, stock compatible fish. Angels seem to have personality as well.
1 Rainbow Shark is fine. Just give it a good hiding spot on one side so it can be territorial and not beat up other fish.
Avoid nippy Tetras. Many are peaceful. Bleeding Heart, Lemon, Cardinals all should work. Large schools look nice.
Another showy peaceful fish is a Pearl Gourami. Not as nasty as the 3 Spot species.
If you prefer big aggressive fish, then that would be a different set up.
I used to sell fish. Now I just play with my tanks.
This is my 55g. It's recovering from some neglect.
Forgive cheesy music
https://youtu.be/AgU-xdgPov8
Current stock
4 Denison Barbs
1 Farlowella vittata
2 Corydoras sterbai ( adding more as I find them)
Oto ( more being added)
14 Neons ( adding 6 more soon)
Planning to add an Angel or Pearl Gourami later.