After a nice chat with someone aspiring to start their newsletter I had several thoughts and suggestions come to mind on launching a newsletter.
#1 You are off to a great start if you want to write about something that excites you, chances are that others like yourself are just as excited.
Set up an account with Substack it's easy.
#2 Knowing who your audience is (based on your interest/experience in a specific topic), reach out to them and let them know you're launching a newsletter on "x" topic.
#3 Commit, commit, commit. I can't stress it enough, set an exact date and time when you will publish your first issue and follow through with a promise to continue publishing at a consistent pace that works for you.
A tip I heard from a podcast before was, A+ consistency with B+ content is better than A+ content with B+ consistency. Be consistent!
By launch you should have a few email addresses from signups, you probably will receive some feedback from them. If not, email those addresses and politely ask for feedback. This is a great measuring stick to evaluate your content's value. Be specific in your questions and ask what your readers enjoyed most, focus on writing about the most common interest.
This is an experiment, test drive it, try new things and be consistent with what works, you will be amazed at what will happen.