the resolution is great, and mostly depends on the controller to be honest.
on AC i see the values being fairly stable at 1/100th of a degree. The same sensors on a Corsair commander pro gave me readings in the +-0.5° range

the only problem you'll run into is they are not really calibrated like thermocouples would be, so there will be variations from sensor to sensor.If you want a precise measurement for power dissipation, i suggest you check them against a TC to enter an offset in Aquasuite so they are matched in their readings.. to get an accurate dT value.
that said, as you said the dT will be small, for the CPU at least, so you'll have better luck, and more precise results, calculating the power dissipated by the rads (rad inlet - rad outlet if they are in series with no block in between). but you can do that too with the setup you want to do.
that would be a way to check how precise your measurements are. the dissipated power from each block should match the power dissipated by the rads

if you have a series loop, you would only need 3 sensors to do all those various virtual sensors.
all rads in series, going to sensor - GPU - sensor - CPU - sensor and back to rads. If the pump is in one of those positions, then that's two sensors only that you need
If you loop rads between blocks, that will require more sensors for intermediate readings

One for air would be very useful too to get the water to ambient temperature difference, commonly used for fan speed control, auto adjusting all year long if your room has no AC (since radiator efficiency is directly related to that value)

you can use any combination if inputs to make virtual sensors, or reuse the same physical sensors several times of course. Any sensor reported to Aquasuite can be used, from hardware ones in the Next pump, temperature sensors, flow sensors, but also the ones from hardware monitoring, HWinfo etc...