I want to hold a competition but I’m not a BJCP member (or maybe even a homebrewer). How do I proceed?

Where to start?   There is a great deal of information on the BJCP web site.    Look at the Competition Center page (https://legacy.bjcp.org/compcenter.php), the Rules page (https://legacy.bjcp.org/rules.php) and the Competition Handbook (https://legacy.bjcp.org/docs/SCPCompHdbk.pdf).     That will tell you a great deal about BJCP competitions.  The Competition Handbook has our best advice.
But what I suggest you do is partner with the local homebrew club and BJCP judges to help organize this for you.    When you register to have your competition sanctioned, we will send you a list of all BJCP judges.   Pick an experienced BJCP judge in your area to set up and run this for the staff points the judge will earn.   If your area has had a BJCP Study class, the leader of that class would likely have local contacts as well. Assistant regional directors for the BJCP may be able to help as well.
You can register, pay and be the organizer or you can get one of the judges to be the organizer.   Use primarily the BJCP judges but you can also use some professional brewers as judges (when paired with more experienced BJCP judges).

Direct whatever specific questions you need addressed to the BJCP Competition Director if your club and local judges cannot answer them.