I feel your pain. I managed to read about 80% of it before my main source vanished. Now I'm stuck on a cliffhanger with no clear way to finish. I'm just lurking in forums, hoping someone will mention a new site in passing. It's a waiting game.
The development is heavily reliant on mirroring villains. He often faces antagonists who are what he could have become—perfectly efficient, utterly detached monsters. Seeing his own methodology reflected in its ultimate, amoral form horrifies him on a level he can't initially articulate. His rejection of them is a rejection of his own worst potential, and each victory over such a foe is him consciously choosing a different path.
The manga is currently my favorite way to experience it. The artist captures the protagonist's deadpan cynicism perfectly in his facial expressions.
As for order, the manga hasn't deviated from the core plot beats of the early light novel volumes. So you can read the available manga chapters confidently. Once you catch up, you can seek out the corresponding light novel volume (if translated) or the web novel arc to continue.
The transition is pretty seamless. The manga ends on a cliffhanger that directly leads into the next major novel arc, so you'll be motivated to make the jump to text.
Burnout is a real risk. The light novel has many volumes. If the anime is a hit, the pressure to keep producing seasons could lead to a decline in animation quality or rushed storytelling down the line. I'd rather have one fantastic, self-contained season that adapts a complete story arc perfectly than three increasingly mediocre seasons that try to cram everything in.
Sometimes, less is more. A tight, well-produced 12 or 13 episodes that tell a satisfying story would do more for the series' legacy than a bloated, ongoing adaptation that never lives up to its first season.
I'm just sitting here refreshing the page, hoping someone has a magic link to a free, legal, ad-free, high-quality source that also delivers pizza. We all know that's not happening. Legit reading means using the licensed apps, which involve either watching ads, paying per chapter, or buying volumes. That's just the reality of supporting the medium we enjoy so much. It's a small price to pay to ensure the artist and writer can keep creating.