Two different numbers answer this, and the smaller one is the one to plan around.
- Up to 8 rbAmp modules on one hub — as many as 56 current channels.
- History and cost for 12 measurement points.
So you can clamp far more circuits than you can keep history for. A channel beyond the twelve still measures and still shows its live power; what it doesn't get is stored records, and therefore no cost, no history view and no CSV.
Which twelve
Pick them for the questions you actually ask. In most homes that's the supply, the big loads that run on their own schedule — heating, hot water, an EV charger — and the circuits you suspect. Lighting and sockets are usually better off left to the remainder: the app shows what the measured circuits don't account for, so a small unmetered circuit isn't invisible, it's just not itemised.
If all twelve slots are taken, the app says so when you try to add another point.
Adding modules later
You don't have to decide at once. Modules go on one I²C bus and are added from the app one at a time — the eighth connects exactly like the first. They ship at the same address, so connect and readdress them one at a time.