Small Subpanel

I would like to install a small Subpanel close to my main panel. I have an 80 Amp double pole breaker that I plan to install in the main panel to feed the Subpanel. I'm thinking of using #3/3 cable as a feeder. The subpanel will contain four 15 Amp breakers for lighting circuits, a 20 Amp double pole breaker and either two single 20 Amp breakers or another double pole 20 Amp breaker. The 20 Amp double pole breaker will be supplying power to 3750 Watts of baseboard heat. The two single 20 Amp breakers ( or another 20 Amp double pole breaker ), will be supplying power to two room air conditioners so, of course, would never be used at the same time as the baseboard heat. Will this be okay?