So, I placed an order to Mouser the other day to actually get some parts into my hands so I can better design the boards.
In that, I discovered the screw terminals I was planning on using, are discontinued. So, I found something that was able to take the same gauge wire: Phoenix 1017526s. Turns out, these will not fit along side the current shunts on the board as planned.
There's just no way I'll be fitting these on a 5×5cm board and have room to spare for a shunt in between. Since this is really application-specific, it might be better off board. We'll put the INA219 and PCA9615 together on the board so we have a nice self-contained sensor board that can be mounted close to the current shunt, wherever that lives, and have nice noise-resistant links back to the controller.
This does mean I can do things like put a current shunt in the fuse box where the solar panels connect, and run CAT5 down to the controller from there.
To make routing easier, I've gone to a 4-layer board. The board has solder-jumpers for setting the I²C address of the INA219, and I've documented all the termination and pull resistors. I'm not sure what ones are needed yet, so there's space at every point where I could envisage one being needed.
There's two power planes in the inner layers, one for VCC the other for 0V.
Next step, I'll print out the board designs and test fit everything before ordering the boards, which I hope to have ordered this afternoon.