Bichirs are indeed awesome fish. Always loved mine. They can eat tilapia but will thrive just fine on regular pellets. The Oscars are not wild caught unless you specifically ordered them that way. I wouldn't worry about pH too much with fish store purchased fish- these are all very domesticated species and adapt fine to tap water. You are smart in my opinion in treating the water as little as possible. In general, the Jewel should be a fine match with Oscars, convicts, firemouths- as long as the tank is large enough. 2 Oscars alone need quite a large tank, what size were you planning on upgrading to?