That's a pretty good start, if that alone it part of the prologue or first chapter (I write a lot of dark themed fiction, so I don't have a problem with characters getting murdered or killed off). It sounds like you can work a lot with character interest based on that alone. Development comes in later, though, after you've already established this part. As he goes about becoming a trainer, you need to planning out where you're willing to go with the story. It's easy to overemphasize the fact that he went through this stuff without showing that he is overcoming the trauma as a trainer. Though, there is always the option of relapse where his memories are so bad that he can't get past it, but I doubt that's what you're aiming for.
There's no real way to justify whether a fanfic is good or not just by talking about it, though. Sometimes the best thing to do is just post part of it and see if anyone's interested. It's hit-and-miss a lot of the time, but usually some people will read it, even if it's just a few.
Yes, the prologue is about him receiving his pokemon from his uncle, which is currently Lt. Surge, and the "trauma" happens at the end of the first chapter. Basically, the whole town (Pallet) was set on fire, and that's when all of this happens. Since this is based off of the original Kanto games, he goes to Oak, asking for a Pokemon so that he can go help take down the "bad guys" that killed his friend and pokemon.
I am trying my best to set it up like it's going to be a "10 year old and pikachu go on adventure", then immediately turn it around into this, in hopes to captivate any potential readers.
Another thing that I wanted to touch on is characters. I am having issues with deciding who should join him on his journey, if any at all. His other friend (for now, named Gary), became a trainer 4 years before the protagonist did, and slightly guides him at the beginning of his journey. The only other character I have planned is a kid that loses his Caterpie, who follows the protagonist for like 1-2 chapters, then most likely leaves. So, I'm unsure if I should have characters that tag along with him, and if I do, should they be characters that people already know, like Misty or Brock, or a completely made up character?