I have 300 gallon ready to go looking to plant the tank add some little fish to cycle the tank then in a month or two add some Oscars and a silver arowana. I've had arowanas before in a planted tank so I'm not worried there but idk about oscars, your thoughts?
No concerns other than adding small fish to cycle the tank. Not a practice i would agree with or recommend, no need, add the plants, add some filter boost and get the tank running for four weeks checking the parameters.
The oscars will probably destroy your plants to be honest, would be better off with big non-cichlids if your goal is to have a heavily planted tank. With oscars the most I usually get to work long term is a bit of anubias or java fern
For my Toni's first birthday I got a her a giant Amazonian sword mother plant. Over a couple months time she ripped the leaves off till there were only three left.