I launched my first SaaS (https://www.wisecashhq.com - cash flow forecasting for freelancers and SBOs) in private beta one year ago.

I enabled the (upfront) paywall a couple of weeks ago and have currently 15 or so paying customers (the early adopters got a 20% lifetime discount).

For marketing, I'm going to use twitter, useful blog posts (educational, howtos) related to cashflow AND how to start your own SaaS successfully.

In terms of getting traction, I think that putting a very basic landing page a year and a half ago helped me get traction - I mentioned the product quite often on twitter while working on it.