I suspect we don’t need exact measurements except for the maximum length of the board. It is just that if some particular pattern would make it easier to do, before the board is layed out is time to do that. I’ll space the sensor pads out across the length of the board. With long leads on the sensors you should be able to tilt them a bit one way or the other before soldering them to fit them where they need to go. it should also be possible to make both a dual row header (looks like about 20 pins all told) and a row of single pads at the back / center of the board so you can use either ribbon cable or wires, which ever works best. All the internal wiring will be traces on the circuit board so it is only the connections to the mega (and power and ground which don’t show on the initial schematic) that need pads.
Peter