Also a rookie mistake to avoid: the contact email address that you provide your email hosting shouldn’t be the domain hosted on that service. If there is a technical problem with a loss of access to emails and you need to contact them,... ask me how I found out!

This I agree with. I even run my nameservers different to my registrar, meaning that if my registrar has technical issues I can still control the domain routing. If the nameserver company has issues, I can still change nameservers.

I strongly agree with this, but I'd go slightly further and say your domain registrar should be entirely independent of any other services.

At one point I had my domain registered through my ISP, which was run rather eccentrically by a gentleman I eventually had a dispute with. He then (probably illegally) disabled all my DNS records, leaving me without my main email account for a week at a particularly vulnerable point in my life. It was horrific.