Switching to Proton from all the other shit accounts was one of the best online services thing I ever did in my life. I got a discount back then and to be honest, I would even pay double the price, if I had to. It's just worth it.
As to what you need to know... There is not much to know, except, just do it. Do not hang onto the obsolete accounts. Migrate everything to Proton, then keep the old accounts for 6-12 months, just to make absolutely sure, you did not miss some rare account you barely ever use and is still connected to the old e-mail address. Finally, just never log into the old one ever again and stay with Proton. Proton is king.
If I remember correctly, Proton even offers migrations features, which let you migrate from Google to Proton in some mouse clicks.