It's short… like a tl;dr for people with the attention span of a Magikarp…
Don't be lazy bro, just… REAAAAD!
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◓⃙. About "strength":
In this book there aren't really 'levels' as such. The way Pokémon 'strength' is measured, at least from Tetsuya's (MC) point of view, is through the "moves" they naturally learn, as well as their stage of evolution. You can roughly use the wiki as a guide: for example, starters evolve at levels 16 and 36, which serves as an indicator of their "strength".
◓⃙. About the world-set:
The world is a bit "darker" and more "realistic". Resources are monopolized by a select few (as always), and Tetsuya, our MC, won't always use the most "proper" methods to achieve or obtain what he wants.
You could say this is a cynical world.
◓⃙.About the "poison":
Now, regarding the "poison"… it's been reduced to a level that won't interfere with the vision and world the author wants to create. We have to accept… certain things, like items, that in such a magical and fantastical world aren't impossible to exist.
Realistically, the only reason they don't appear in the games or the manga/anime is because they'd be too difficult to balance and overly complex. I mean, there's already the "Rare Candy" to level up, or the "Vitamins", also de held items… is it really that hard to imagine other items that could boost a Pokémon's "attributes" or "types"? People, let's not get carried away by the hate!
◓⃙. Guide for you, my bro:
"Dialogue"
'Toughts'
[Systems, Special Moves, Special Tags, Special Pokémon, Voice through devices.]
"Telepathy" Italics for telepathy
"Whoaaa!" Bolds instead of CAPS for SHOUTING!
◓⃙. ALMOST FORGOT!!!
Tetsuya (MC) doesn't focus only on Poison-types, he has several others. It's just that in the "previous timeline", that was his specialty and he became skilled at it. Any normal person would start with what they're good at and then expand into other paths (Types).