Sooo.. I may have opened a can of worms with regards to something I may not be fully prepared to go down the path of.

Allow me to explain. My kids are reaching the age where there are now at least a few annual stage performances and being away from family, it's something nice we'd like to share with them.

My interest remains in photography and in events such as sports, I still think that is my preferred medium to record.
However, stage performances is a different story IMO.
Last year at my daughter's ballet performance I shot stills and relied mainly on the purchased professional DVD for the video. My wife also had a smartphone video but the trouble is the purchased video included pans and selective edits so footage of your own child is very limited and of course smartphone videos are poor at the distances we're at.
This year, I shot a video. I think it's the first time I've actually used the function for anything I wanted to keep
And of course the video quality as well as centre of focus was far more desired.

Come editing time, I realised I only had the included iMovies software and it did a reasonable job at outputting a final product I could post to the family, which they really enjoyed.

Here comes the worm bit. The RAW photographer in me wasn't really satisfied with the limited processing and final results. I know the final audience of the videos won't really notice but the curse is, I do and I care about these things.

The good news is my camera is very video capable so no additional expenses are required on that part. The bad news is whilst my (very old by electronics age) computer does fine for stills, it was woefully inadequate for video editing.

So I need some advice on basic video needs to see whether to go down this path. My camera is the Panasonic G9 and the intent is to exploit the maximum the camera is capable of, which after the recent firmware upgrade is quite substantial. So I'll be recording in 4k 60P but editing down to a manageable file size.

Computer: Unfortunately I'm limited to Macs because of the whole ecosystem thing. I have an inkling it's video card and GPU RAM that I need. Anything else I should be paying attention to?
Software: So, again must be Mac compatible. I only know of Final Cut Pro but what else should I be looking at?
External recorders: I like the idea of recording to a separate recorder so my internal cards are for stills only. It also has the advantage of higher quality output I believe. I'm totally new to this so any brand recommendations as well as maximum compatibility as I will likely have future, non-Panasonic cameras with video capabilities.
Sound: Do I need anything other than on-board. We're talking stage performances here so I can't get any closer anyways.
Misc: Anything else I've missed?