Ask HN: Best WordPress practices for small biz: security, themes, plugins, SEO

I've signed up to build a WordPress site for a small NLP company in the EU. They want a minimal online presence and competition is high. They're hard-working, but old-fashioned, don't use automation a lot. I am sort of supposed to also do marketing & SEO stuff, but I can't imagine how to differentiate them well without a software product in Python.

I had a little experience with WordPress, and would like to build a minimal professional looking website with minimal costs (free themes & plugins). I generally wouldn't like to focus a lot on WP back-end, SEO, but would rather focus on stuff for which I actually signed up for this job - learn & practice more Python.

Assuming that my hosting provider ensures server-side security, what are the best WordPress security practices for starter admins (apart from strong passwords, 2-factor authentication, not installing shady plugins or too many of them and keep updating everything in WP)? What WP themes & plugins would you recommend including SEO automation?

If possible, what can be the best SEO strategies, if a dozen of top ranking competitors are all the same professional and high-quality? I am a beginner and generally would not like to focus too much on SEO, but I've complied a list of keywords for my niche, with highest search volume and from Google search.