As someone else has already stated, live feeder fish are not a good idea because they introduce parasites and disease. Feed your oscar a quality pellet staple and supplement their diet with frozen foods (silver sides, krill, and very occasionally beef heart). Although some people swear by it, I stay away from terrestrial based foods so beef heart is not on the menu for my fish.
Plants will, unfortunately, not do well in an Oscar tank because they are prodigious diggers. I would also suggest extra suction cups on filter intakes and I would probably invest in a plastic or metal submersible heater as Oscars are notorious for biting, shaking, and eventually breaking glass heaters.
The issue most aquarists fail to comply with when owning Oscars is water quality. Oscars are large messy cichlids. Overkill on filtration is a good idea and weekly water changes are a must. Poor water quality will result in external parasites and disease. "Hole-in-Head" is a common ailment of the Oscar who lounges in dirty water. Tank size is another issue. One Oscar should be kept in a tank no smaller than 55 gallons (some would argue 75 gallons is the minimum). They grow amazingly fast given proper tank space, diet, and water quality.
Best of luck!