Modbus binding has no idea how to deal with C, kW etc. units as they do not exist in modbus registers, these are just numbers.
There is more than one way to add units manually to your data and pass to a Quantity aware Item type - if you are already using a JS transform in your Modbus data Thing it is probably easiest there.
To control display of units and decimals, you need to look at your Item metadata / stateDescription / Pattern, and use something like %.1f %unit%
