Advice on the right sensors/probes for Ariston boiler + solar panel

Hello, I have the following hardware:

Boiler - Ariston Genus Premium Evo 24 FF (it’s a condensed central heater)
Solar Panel - Zantia vacuum tubes collector
Temperature Difference Controller - STDC-V1 by Sorel
300LT Ariston Electric Storage Water Heater

I’d like to measure/understand my solar energy VS gas balance, but also keep tabs on errors/faults on the boiler (which is not that uncommon sadly).

What’s the best place to start? Thanks in advance!