I'd like to connect PT100 to the core

General
10

Hmm, so I'll admit I've never used a Platinum RTD before... I guess it's more accurate but slower than a thermocouple:

Cheap thermocouple amps:

With SPI to take the error out of the A/D conversion that you'll likely experience somewhat:

Or maybe +/-0.5°C DS18B20 is the way to go: