18 month plan to create a niche course selling site

I am seeing quite a bit of success in a specific niche (personal finance, investing) and I want to set myself up to diversify / branch out in 1 - 2 years.

I understand that selling high-ticket courses is all the rage in blog monetization these days, and this niche is surely a good fit for it. Does anyone have some recommended resources for how one can build a good niche / authority-site in approx 18-months?

I expect to get some excellent PR-opportunities going forward (think Podcasts, interviews, newspapers, etc), and I want to capitalize on this. I am not looking to monetize now, but in 18-24 months, but I want to start laying the groundworks now.

My biggest concern at this time is getting backlinks to my content (as I understand social media shares doesnt count). My current blog lacks both content and a specific SEO-strategy.