Lighting, Light Fixtures, Ceiling and Exhaust Fans - wiring for bathroom ventilation fan/light

I am adding a badly needed vent fan with light to my bathroom. There is currently one wall light fixture and I am hoping to add the fan to function on the same switch as the existing fixture.

Here is my first (uninformed) plan for how to wire it...

The existing light has power run to it, not the switch box. Is it acceptable to add a junction box essentially splitting the switch loop by wiring the blacks and whites together for the two fixtures + the switch loop? Will this work, or do I need to do something else? I am checking the library for wiring guidance tomorrow (plus a former electrician co-worker), but thought I would ask here as well.

I hope I have clearly enough explained the situation and my plan to wire. I apologize in advance If I have proposed something entirely wrong.

Thanks

I didn't understand you exactly but if you have a switch loop you could just change from 2-conductor to 3-conductor cable. The single switch you have would be replaced with a duplex switch.

The black of the 3-conductor cable would be connected to power in at the light.

At the switch the black would go to the side of the duplex switch that has a brass tab connecting the screws.

The red would go between the fan black and one of the screws on the side of the switch with no tab.

The white wire would be recolored on each end blue or some other color except white or green. This wire would run between the light black and the last unused screw on the side of the switch with no tab.

Grounds connected in the normal manner.

Thanks for the input. Sounds like my understanding of what was needed was not correct, just as I suspected. I was hoping to avoid pulling cable.
I will go over your input with my "consultant" and pick up the book to educate myself some more.