Lighting, Light Fixtures, Ceiling and Exhaust Fans - Adding new wall switch for ceiling fan

I have an existing wall switch that controls the top half of wall outlet. The wall switch is made to expand, since the box is sized for 2 switches but has a single face plate.

I want to leave the existing switch controlling the wall outlet, and add a new switch to control a new ceiling fan I'm installing.

I think I can figure out the wiring to the fan and I won't touch the wiring to the wall outlet. But I want to make sure I wire the switches correctly.

Coming into the existing wall switch I have three white wires nutted together, 4 black wires nutted together with one of those blacks going to one side of the switch, and a red wire going to the other side of the switch.

Do I just add another black and white to each nut of the same color and connect those new wires to the new switch? Something tells me it can't be that easy?

Thanks in advance. Joe

You are wrong. The breaker would trip as soon as you turned on the switch with that setup. You add the new white wire from the fan cable to the other white wires. White does not go to the switch in this case.
You add another black to the group and connect it to your new switch. The black from the fan goes to the other screw on the switch.