Best platforms and practices to start automation testing of a fully system (HW, SW and FW)?

I'm studying test plans for a complete system with an in-built firmware code that communicates with its software developed in electron and a mobile app. I would like to invest my time in building a strong automated test plan but I'm a beginner in this automated field and I'm a little bit lost in this world with a lot of available software. Should I select different platforms according to the type of code I'm testing (for example, selenium for software and others for firmware?)

Is there anyone who can give me some guidance about the best practices for the right software choice?

Thank you!