GoPro pros:

Wide angle, 4k. Easy to get the whole band in, in a small room, and the 4k gives you four HD cameras worth of data, meaning you can zoom in 4x and still have HD pixel density. Since bands play on single level stages, this isn't strictly true in practice, but you can zoom further with 4k than HD before pixellation is as noticable.

GoPro cons:

Battery life, SD card capacity, necessary placement due to wide angle, necessary accessories.

At maxed video and audio settings (RAW audio) i got around 45 minutes before the battery died. I get about an hour with standard audio recordings. I don't even use the onboard audio, so no loss there.

With a 10 Ah external battery, I get about 90 minutes of recording time before the internal battery goes dead. The charge limiting circuitry does not keep up with the discharge rate.

You need big SD cards. 256GB or larger, and they do not swap quickly.

To full frame a typical band, the tripod needs to be around 6-8 feet back from the lead vox mic stand. On an SL-100 stage setup, up against JBL 828 subs (vibration) and out in the "dance floor" area. Big gigs get tripods kicked or moved out of adjustment.

Accessories, you don't get a standard 1/4" by 20 tripod adaptor. $6. You need extra batteries. $20-30 each. An extra charger, $40. Extra SD cards, $40. A "trap door" battery cover, if you plan to use external batteries. $20. The front element of the lense and touch screen are no longer replaceable, and need protection. $10-20. You can save some money here, IF you run a fleet of GoPros instead of just one.

As for lighting... anything besides a tuned lightshow will lower video quality. Ideally, you want mostly white or pastel front washes, properly dimmed to match camera exposure levels, then a back line show with commensurate brightness to match the front washes.

Limited exposure ranges will tend to make all but the very front audience rows dusapoear into darkness unless the backline blinders are on.

The lower the level of light you work with, the grainier your video will be, and less expensive sensors get grainy fast in low light.

HDMI capture cards start around $100, but this level is marginal. Magewells go $300-400, offer better performance, and can drive an HDMI cable over longer distance without freezing. Past 25 feet, HDMI gets iffy, unless you use... the right... HDMI to Cat 5 systems. Trial and error there.

Black Magic's ATEM minis offer a control surface and three HDMI inputs for about the price of a Magewell capture card, but I haven't used them and can't comment on quality or reliable operation.

At pro levels, video travels over SDI.

THE advantage of cams like the bmpcc4K on m4/3 is that you can actually work with cheaper lenses, as f4.5-6 is what you need to have sufficient depth of field (for larger groups). Otherwise only one subject will be in focus.

In this case, I find for most indoor concert settings (mainly classical music for me, so not much light), the second native ISO of 3200 almost perfect.

If I use more light-gathering lenses, I quickly need to go towards ISO 400. Which is where most "normal" camera's look decent.

If you need cheap, good looking lenses, get Kamlan. I have the 21mm, 28mm, and 50mm f1.1 (!!). They are really nice (soft/dreamy) wide open, and razer sharp (modern) from f2.8. Budget = 200-300 dollar a piece ... full metal construction.

Thanks for listing the GoPro cons. The battery life seems to be the biggest limitation there. I was looking at the Zoom Q2N 4K, and it gets round this problem as an additional battery case can be added, allowing it to be powered off AA batteries, giving up to 4 times the recording time,. It can also be powered off an external USB power bank.

Can GoPro not work off a USB power bank or the mains?

Yeh, I've looked at some reviews of the Zoom Q2N 4K and several people have said the video gets a bit grainy in low light. Oh well, you can't expect perfection in that price range I guess.

Is a capture card so you can record video to a laptop (via a camcorder) instead of to the SD card on the camcorder? If so, is there any advantage to this? I guess computers have bigger capacity than SD cards so that's one advantage.

One advantage to capture card over SD is live streaming. Another, depending on how you set up, might be avoiding having to sync files in post.

The GoPro works fine off a power bank, except it still discharges, just more slowly. Rough figures in my previous posts.

Can't you just plug the cameras into a computer via USB for recording and/or live streaming?

How long is your USB cable ?

https://www.youtube.com/watch?v=q9MIeO_pdgk

I can't speak to Gopro per se because I've never streamed with one. Generally, cameras output video signal over HDMI which has to be converted to be fed into a computer USB port via a capture card or HDMI to USB converter. There are inexpensive (under $25) converters that work. https://www.youtube.com/watch?v=EAKns_MF4NQ

The thing to watch for is that the camera will output a "clean" signal that doesn't carry information that you typically see on a video camera about the battery level, mic levels, aperture setting, etc. Tends to be the more expensive models that have clean signals.

If the Gopro doesn't have the battery life you need, there are some camcorders that can be powered via an external cell phone battery that will enable longer recording times.

A decent quality two camera protocol will move you well beyond Inexpensive. I use two GH5s with Atomos V recorders and feed the stereo SR audio with DX32 Prime outputs. I have the free Davinci Resolve 18 video editing suite that has a rather steep initial learning curve, however no where near as difficult as Pre. Pro.
Lou Judson raised some very important concerns pursuant to lighting and shot framing. To this end the GH5s work pretty well with most stage lighting and a 35/100 lumix lens on a stand alone unmanned camera for a continuous full band shot. The active close ups and lead shots are with a 12/35 lens manned camera. I work with H265HD 1080P 24 frames that edits pretty well and with DNxHD deployed for rendering a 265 codec for distribution is easy to do. I have been working with this basic video structure for more than five years and the editing challenges keep me on my toes. The plan you have advanced will most likely turn out to be a less than successful video editing nightmare.

Imo you can achieve acceptable results with low/medium budget gear if you know your equipment. Three videos I have shoot/edited:

Gear budget approx 3000€. Concert multicamera. 6x cameras, 5 stationery and one moving (my wife operating, I was playing drums) GH5, DMC-G80, GoPro4, 2x old EOS M with kit-lenses (you can get these for 100€ body 100€ kit-lens, they do fair quality full-hd)
https://www.youtube.com/watch?v=vIU8xjLj9kg

Budget approx 500€ (music video I did for my friend's band)
1x eos m with kit lens, 3x lights, black molton-canvas as background
https://youtu.be/LwVRqJd7EIk

Budget 0€ (!) I just asked the festival organizers after our show wether I could get my hands on their multicamera files. I got the full show and edited a promo for our band, yay.
https://youtu.be/gU-JOcCe118

That's awesome sound and video quality you have there, especially in the Doors tribute video! Now I'd love to know what you used to mic the drums, and I presume the audio was all recorded through the desk into a DAW then mixed/mastered afterwards?

Yeah the audio was from desk, just a stereo track straight to usb-stick. I equed it, did some compression and blended in some of the space ambience and audience from one of the cameras' mics.
I can't recall the exact miking, all that was done by the house engineer. But something like the usual 57 on snare, propably 414s for overheads, 604s on toms, 52 on bassdrum, something like that. I usually prefer wooden snaredrums but for some reson I took the Ludwig Supraphonic with me that day which I think was good for the articulate drumsound.