> I was thinking about hacking up a clip-on ammeter

The easiest spot is right on the distribution wires, they usually are pretty beefy and that means you don't have to re-hang your meter after every breaker. They're also very well insulated so the chances of shorting something out diminish a lot (but if you do the effects will be far more spectacular ;) ).

In the end I installed a 'Shelly' three phase current meter permanently with the pickups around the mains wires. That gave me very precise logging (and given that the distribution board passes those three wires roughly balanced out across the breakers it is already quite fine grained). It also allows you to spot intermittent consumers and for the money I wished I had installed it earlier during my hunt.

Oh, as for laptop: I ended up buying a second hand W540 which is pretty beefy when you want it to be but normally it sips power (about 29 watts continuous draw, the screen is off because I have two external monitors connected). Oh, and about those monitors: I've reduced the backlight intensity from the default quite a bit and that made a real difference as well (besides the usual power saving and desktop lock settings).