question

@TomF

Usually with multiple devices you get a GX then it co ordinates everything in the system.

If you dont want to buy a Victron GX then you can make your own one with a Raspberry Pi.

You only really need a temperature sensor if you have lead acid systems that needs temperature compensation in charging. Or do you jave another reason for needing all the devices to have one?

I think @WKirby answered it well in you first question.

A little background about temperature compensation with AGM cells. When temperature drops, charge voltage is increased. So units will adjust charge voltage up or down as needed if there's temperature compensation. If temperature rises, voltage gets reduced. For an increase temperature, reduction in voltage is very small. Default is -16.2mV/C. So an increase from the standard 25C to a very hot day of 10C means a reduction in charge voltage of 162mV or 0.162V. For winter, the opposite applies.

The Multiplus comes with the necessary sensor.

MPPT doesn't, but effectively it won't be charging in winter, so can be ignored.

The Orion will only be working when the vehicle is running.

So simple, cheap solution: set MPPT and Orion absorption voltages to the low end of the range (e.g. 14.2V) to allow for summer. Set Multiplus correctly. For winter either ignore the slightly too low voltage from the orion, or just increase it slightly if you expect to be using that for most of your winter charging. You don't need the extra cost or overcomplication, what you have already specified is enough.