> A lot of startup advice is vague.

Sure, but in an ocean of quantity you need to know where to look for quality:

1. https://www.startupschool.org/

2. Book: The Lean Startup.

Those 2 resources address everything you need to know and then some, with concrete advice.

> What channels worked?

You have it all wrong.

I’m documenting my exact process of this here: https://opus.cafe/goal/jj/26#progress-6

Still a lot of learning to go, though

I usually don't start anything before I know where to market it. So the first 10 or 100 users are usually day 1 after the first one or two public posts.

That likely doesn't help other than, think about where your customers are