Just use the iso you need to get the shot. A good photo won’t be ruined by noise.
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Agreed. And the sensor is great so you'll probably be pleasantly surprised. Just set the max iso to 3200 or 6400 and let the camera do it's thing.
On the other hand, I'd say worry more about metering mode (I'd stay away from highlight priority because of bright artificial lights), and focusing (autofocus will be trash in low light, so you'll probably have to zone/snap focus a lot).
Not a GRIII user, but the 24MP sensor is pretty well-known and I and people I know have used cameras with that sensor. I'd say ISO 3200 is definitely doable. ISO 6400 will need more care. ISO 12800 in absolute emergency, and will require very very careful exposure and post-processing.