This is exactly what I do, and it's worked beautifully for me. (domainname)@mydomain.com is pretty standard/easy, and storing it in password manager makes it even easier.
Same here. Sometimes I'll also add the date when I entered the address in a form. For instance, the last time I registered to vote, I used YYYYMMDD-ca-voter-registration@mydomain.org. During the last election cycle, I caught a few California politicians harvesting my address and adding it to their email lists.
Ironically the CAN-SPAM Act only prevents commercial entities from doing this, however shady the practice may be. Political emails are protected free speech and AFAIK the means by which addresses are obtained is irrelevant.
Not the poster you replied to, but I use Fastmail.
If your Fastmail address is dfinniger@fastmail.com then you can randomly create emails like:
some-domain@dfinniger.fastmail.com
and it will automatically send them to your main email.
It's very convenient, and the cost per year is likely to be less than your hourly rate multiplied by the number of hours it'd take to set up self-hosting.
I use G Suite for one domain (because I was grandfathered into a free plan) and Zoho for others. IMAP is a little faster in Zoho, and I haven't seen a difference in reliability. The Google web interface is much better, though.