A couple of more thoughts.
I was using a GoPro Hero 3 Black. Still have it, but upgraded to a "proper" camera a few months ago.
With a Hero 5, I would definitely just start with the camera only - no cheap lights - and see how it does. Mine gets pretty decent video, even at depths >60', with no filter. I will use the filter I have from now on, though, and I expect it to do even better. For depths less than 60', I think stills (through a filter) would also come out pretty good - assuming the water is decently clear and there is SOME sunshine getting through.
Also, if you do get a tray and mount a light or two, just keep this in mind. That Loc-line stuff will come apart. If you use it, you might want to consider either getting the kind that has a leash run through the center, from end to end, so if it gets knock and unsnaps in the middle you don't lose your light. Or, use some kind of line and put a leash from the tray to the light. Whichever. I just know at least one person whose Loc-line came apart as they were getting back on a boat. They think maybe it was during the hand-off of camera to boat crew. Regardless, my friend lost a light that way.
I bought this tray to use with my GoPro. You can remove either (or both) handle, if you only have 1 light and want to reduce bulk.
https://www.amazon.com/gp/product/B00WSLDRW2/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1
For coming with 2 handles and 2 clamps, the price seemed very reasonable. And now that I've gotten a proper camera and some strobes, I'm using the same tray and clamps, with arms and more clamps added. No need to replace anything.
Initially, I just got one of these, to mount my Archon video light:
https://www.amazon.com/gp/product/B00Z09CCJI/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1
I took one handle off, so the GoPro on the tray, with one video light (which, like I said, only did anything within about 3 feet of the camera), was my rig for a while and it worked well without being annoyingly big.