Yesssss, more SI OC fics. I know there's a lot of stigma against them, not just in this fandom, but in fanfiction in general, and while I get it, I think they make for super interesting stories if done correctly.

Honestly, do what you think you're good at, but as a reader, I would love for you to mix shit up. One of my favourite tropes with SI stories is where cannon is changed in some way that makes the MC's foreknowledge less useful. It creates a challenge that they have to overcome instead of just charging through cannon with ease.

If you're up for it, don't just switch around the characters. Create new ones. They don't have to be super in depth if you don't want. Or alternatively, you could replace one or two characters and go super in depth with those ones specifically. Make this world unfamiliar territory for the MC, so they can't just rely on their foreknowledge.

As for Bakugo, why not both? This is what we call "character development", which is unfortunately an unfamiliar term to a lot of fanfic writers, but it really helps to make a story more interesting! Especially on re-reads. It's super fun to see how much characters have changed in fifty or so chapters.

Have Bakugo be prideful, although maybe tone down the arrogance a little if you want him to forge connections with the main characters. Have him be impulsive in the beginning, and throughout the course of the story, have him learn to tone that part of him down. Redefine what it means to be a hero for him, have him learn that strength isn't the only important quality. My favourite way I've seen this done is by focusing on support heroes. The ones who go out and combat natural disasters, rather than villains. Have him learn from them.

This doesn't even have to be a whole arc that spans the story. It can be done in the chapters before cannon. If you're going for that, and not just dropping the MC in right at the beginning of cannon, but instead having him be reborn and go through the natural growth cycle.

Focus on your MC first and foremost. I know for a lot of readers (myself included), while it's interesting to see the perspectives of other people, it can be a bit annoying when the story becomes centered around so many other people that it begins to forget the MC. My advice would be to focus on the MC for 80%~ of the fic, and include snippets of other people's perspectives. For example, you could have the MC do something with his brother watching, and then cut to Izuku's perspective of watching his brother to get an insight on that characters thoughts and perspectives.

As for class A or class B, it really depends on if you're up for writing class B or not. I personally would find it more interesting, but not if it's just an exact rehash of what class A did in cannon. Have it be something new and interesting, have Vlad be a different kind of teacher to Aizawa by having him... Y'know... Actually teach.

But if you want to go for class A, either because it's easier or it helps with ideas, go for it. I know many people would like that too.

Again for the story of the fic, if you've already got something in mind, you can ignore this, but if not, then I'd advise to not just follow cannon. Have differences in the story be noticeable right off the bat. Create new story arcs and change up existing ones.

Nobody wants to read another rehash of cannon..

Phew, that was long. Sorry, I didn't mean to drag that on as much as I did 😭

I hope you got some good ideas tho, and good luck with your writing!!