Ask HN: What are the most important resources to learn as lead of operations?

We are a small (~50 persons, mostly juniors) 4 years old software shop that do outsourcing mostly. The senior team have development and QA background with good skill and experience, done >20 finished projects for both start-ups and enterprises. Those are to say that we do have the skills and experience on getting things done and get the bucks.

I did most of the DevOps for the company, and I did get the job done, as in, project A requires an AWS setup with K8s, Lambda, CI/CD,... , I can setup that, no big problem with help from Google. So, in the middle of last year, I got promoted from Senior Full-Stack Engineer to Senior DevOps Engineer, Head of Operations (with operations are everything outside of dev and test).

I've been struggling since then, as the only DevOps guy in the company and no experience/mentor in this role, I don't really know what to do. So, after 1 year, I have almost no progress and nothing to promise, leader understood the situation and didn't push me much but I still feel pretty bad.

Some of the areas that I'm stuck:

- Direction: as we invest more in our own SaaS, I don't know what need to be done outside of getting the thing running on production and watch out for error and outage and SSL expire.

- Certifications: I heard about ISO 27000s, NIST xxx, ... but what certificate is the most important for organization/product, what need to get first, roadmap,...

- Training: I need to train new DevOps, but I realized that I'm doing it really inefficiently, asking the juniors to watch Udemy courses and practice by themselves get to nowhere now.

- Conformity: when working with enterprises, you usually get those big questionnaires and request for documents of network/asset/data/... security/policy, we got over by asking for example documents and fill it in. Now I know I need to write those anew for our organization, I don't know what is needed.

- Adaptation: most of my new tech knowledges came from Hacker News, reading the articles. Is it an efficient way to know the latest trends, newest vulnerabilites,... ?

- Management: I wrote my first yearly report in only 1 page, team and I expected more information but had no clue what else should be in there. I'm also not sure all the areas I listed out here are all there is, could have missed something big.

So, what are some good, important resources to learn in this new position that can help me overcome those issues?