Almost any healthy male betta will flare at his reflection so that doesn't mean he's aggresive at all. Cories are shoaling fish that need stocked in groups of 4-6 at a minimum. Panda's get too big for a 10 gal IMO, but you could do a pygmy cory such as habrosus, pygmaeus, or hastatus. Those are typically pretty hard to find in shops, but pretty easy if you can order online. Another bottom dweller you can do in a 10 gal, if it has a smooth substrate, is kuhli loaches. You could also do something like 6 ember tetras, or neon tetras, or dwarf pencilfish, or dadios/orange hatchetfish. Livebearers like platties and endlers would be an option as well.
