Jake, I know you don't want to hear it, but your tank is pretty much stocked. Platies get large and can be messy fish, so that limits how many you can have in a tank. I wouldn't add a betta, they need special foods such as betta pellets or blood worms. Bettas should not be eating regular tropical flakes. Every betta I've had has refused to eat flakes, so I would question Sclab's assertions that it will eat flakes. I would not add anything else to your tank.