Most replies are going to be from sellers or gurus. I would suggest you DO NOT outsource link building or buy packages at any cost.
Each niche has random ranking factors; therefore, strategies depend on many factors.
Buy basic SEO tools like GSA SER, Xevil, or even Ranker X, and you can do it yourself. This way, you have full control. You can use OpenAI for high-quality content. You can nicely set up all the data you want, like making sensible comments in case you are going to blast comment platforms. You have full control when you create article directories and wikis.
Contextual and non-contextual links both have their own value, so don't underestimate them. I see many replies from Reddit or similar groups getting those links as SPAM. Please don't use them as SPAM; it depends on how you are going to use them.
Since you already made some buffer sites from high DR sites, you are perfectly safe to build tier 2 links, but not 30K at once—just go slowly with nice content. I am pushing 100 verified contextual links and running through a few premium link lists via GSA with the bad words filter enabled. I am having great results with chosen niches.