I am going to try using a GoPro 10 for stills and video at depths up to 120'

I have never had good luck with dive lights. Most likely I have never spent enough money on one...

What would be a good light to use with the GoPro? I plan on using a tray for the light and camera.

I have been considering this one.
Sea Dragon 3000f

I'm using an HID Light Monkey with a reflector and an older GoPro.  My buddy has the same light.  This is how it does in the complete darkness.
https://www.youtube.com/watch?v=dpntPcnWVzg

I haven’t been into that for a decade but what my friends and I would do is make a diffuser to slip over our lights since high power dive lights tend to have a very tight focus. You can make a diffuser easily using anything from commercial diffuser material to a Pringels can lid. I cut mine to fit in a piece of PVC that slipped over my light head and held in place with a bungee chord so I could slip it on or off throughout a dive as needed.

Commercial diffusers are available now for a number of lights. Not sure if they were available back when you were diving.