I'm like half-asleep with a headache and frozen fingers, so I'm not going to give a lot of advice. But I didn't want to leave you with nothing. So I'll just cover what I can explain now. And feel free to ask for any clarification!
1. To me, having a stronger rival will give your OC something to strive for, if that would make sense as one of his goals. Then at the end if your OC defeats Barry, it'll show how far he's come as a trainer. To use the anime as an example, it's kind of like how Ash couldn't defeat Gary at the end of the Orange Island arc, but defeated him at the Johto Conference. Showed in a way how far Ash had come as a trainer and how much skill he gained.
I mean, your OC just started his journey, right? So of course he's going to be a bit less experienced than Barry, whose canon back story would have him make sense to be a better trainer, given who his father is.
2. Remember that there's more to Pokemon battling than just type match-up. Take the Pokemon's stats, their "level" (how skilled they are battling), what attacks they know, how their attacks can combine, and how experienced the trainer is not just in general battles but also commanding the particular Pokemon.
5. While you don't want to stop the battle to describe the Pokemon's attacks, you'll want to describe them to make the battle interesting. Instead of just saying "The Arcanine used Flamethrower", say something like:
"The Pokemon charged towards his opponent. Fire licked at his lips, curling through sharp fangs. With a sharp bark, Arcanine unleashed the attack. Flames swirled and grew around the opposing Pokemon. There was the sickening smell of living flesh burning."
And it depends on what you mean by "lack of detail." I do agree that it makes sense to not fully describe Pokemon (here's an amazing post that gives better advice on that subject), but you don't want to completely skip on every detail. Doing that risks leaving the reader behind in confusion.
If you want, I'll take a look at your fic. OT fics are my favorite fics in this fandom. I'll be able to help you out more if I see how you're writing this fic, compared to what you're writing (if that makes sense).
Hope this helps!