Love the pokemon choices

A good start for a story, I look forward to reading more! :)

I actually don't really have a suggestion for any specific Pokémon as of now, apart from maybe having Eevee either evolve into an Espeon or Vaporeon? I'm rather open on that front, though, since I pretty much like all the Eeveelutions, lol.

But as far as Ash's team goes, I'd suggest not actually giving him too many Pokémon. Personally, I really prefer set teams who then really grow together, both personally and strength wise. Depending on what the maximum carry limit will be in your story, it will probably still be too much to ask to limit Ash's Pokémon to something between six and eight Pkm in total.
But still, no more than a dozen, or so I'd suggest at least. The game feel might get too much otherwise, to the detriment of the charm of a story. The collector and completionist mindset of the games often doesn't do a story that is more focused on a kind of character development any favours, you know?

The thing is, when Ash has too many Pokémon, for him to keep his agency and advance within the story and storyworld, he gets too "strong" while everyone else gets too weak. There's no real struggle anymore, and thus things could get boring. It's of course also a matter of pacing, but let's be honest, you nor hardly any other writer will let Ash trudge through Routes for weeks and weeks to train.
Which means that the time Ash spends training each Pokémon and the strength they gain from it is very unreasonable compared to other trainers, especially those Gym Leaders who were in office for decades already.
Speaking of Gym Leaders, I personally like the concept that they have a personal, (at least) close to Elite 4 level "League" team, while battling challengers with weaker Gym teams according to the number of badges a challenger possesess, very much. It makes a lot of sense to me within the boundaries of this storyworld.

Doesn't mean you have to implement any of that, just food for thought! Anyway, I look forward to reading more. :)

(Ah, btw, one tiny thing: in chap. 1 you stated that Eevee looked a bit like a cat; the Eeveelutions are actually roughly modelled after a fox, as far as I know. It's not an important detail, but I thought I'd mention it while I'm at it.)

Well, the story has a good base and a desirable start. Notice some mistakes here and there, but nothing serious.

The descriptions of the pokedex I suggest you only give it with respect to the basic data of the pokemon and not its movements and abilities. This will give a little more intrigue. Do not overdo Ash, there is nothing worse than a character who receives fools just because.

In the pokedex descriptions, I suggest a different format.

: This pokemon bla bla:

And it is highlighted in bold.

Ignore the critics about the team. Many are accustomed to overrated and powerful pokemon in the competitive. They simply forget that there are another 600 and so many creatures that in anime, manga and fanfiction they can be used and exploited much better.

A shiny Ekans is certainly something unique when it comes to pokemon for Ash. If I can suggest Give it a Zubat. Many pokemon need more love.

Please, don't turn Ash into a Gary stu that wins everything easy, with pokemon that fortify ridiculously fast or with too many pokemon captured each chapter. It simply kills all progress and credibility.

Leaving that aside I wish you the best of luck with your story.

Ekans? Even if it is shiny, it is strange to think of Ash having one—first time I have seen a fic have one. Just how different is his team going to be? Eevee, shiny Ekans, what’s next? Not sure if this story is for me.