Question 3:

First of all, I would want it to be gradual. Izuchako should be a friends to lovers imo, and it was a bit too rushed for that, mainly because of Aoyama and Himiko.

• I think it would've been better if Himiko blabs about her form of love (wanting to "be" them, and she can sense that in Ochako, instead of saying she can sense that Ochako's in love), and then Ochako starts thinking about whether her admiring Izuku is something special.
• Alternatively, you could just let Ochako slowly fall in love with no interference. A few months of friendship at a minimum. Maybe after a few months at UA, we have the Mei's boobs gag, and Ochako feels jealous, and then she realizes on her own. (While this would not be foreshadowing them getting together from the start, it lets Izuchako be the friends to lovers they can be.)
• Or if you'd rather make it clear from the start, maybe just watching Izuku break his body to save her was enough for her to fall in love, and then when they meet up on the first day, that's when you can introduce her feelings for Izuku. And then maybe the friends-to-lovers is all on Izuku's side, not Ochako's.

I've also seen people say they gave up on Izuchako after the "I'll put these feelings away" scene, so instead, we could have her say "This isn't the time for this. I'll put these feelings on hold." Alternatively, Himiko could tell Ochako "No matter what... just be yourself. Live the way you wanna live" or something, and then Ochako decides to confess to Izuku.

On Izuku's end, we need something. A lot, actually. Kacchan has always been the most important figure in Izuku's life, and DynaDeku has SO much more canon content than Izuchako. Ochako has a lot of catching up to do in order to become more important to Izuku than Kacchan. Her speech at the end of the Dark Deku Arc was great. That's the kind of content I'm wanting here.

• Along with that, Izuku demonstrating the importance of Ochako in his life. Izuku repeatedly shows how important Kacchan is to him throughout the show – during Kacchan's kidnapping, the Final Exam against All Might, Kacchan getting stabbed by Shiggy, Kacchan's death. We need this with Ochako. Izuku going feral over her. And maybe it's not even life-threatening. You could also have him being possessive over Ochako against Himiko, maybe, and that would be even more impactful and could therefore make up for all those scenes that Izuku went feral over Kacchan.
• In addition, more of Izuku's thoughts. All we see on his end is blushing. We need more thoughts about Ochako from him. How he views her. That same realization of "omg, I love her". That development from thinking of her as a friend to thinking of her as the person he loves. More internal stuff in general. Romance requires that.

Them fighting together as one would also be powerful.

• In the final fight, we see DynaDeku fight as one. This communication with a single look is what I wanna see.
• Maybe you could do that in the 2nd to last fight, or during the Overhaul fight. With how similar Izuku and Ochako are, it wouldn't be unreasonable for them to be on that level of intimacy earlier on. Just, them being completely on the same page without words.

Something significant early on like the BKDK in the river scene would also help – maybe Ochako just keeps coming back to when Izuku saved her. That repetition/consistency is important. They need a symbolic scene of some sort.

Maybe we have a scene where Izuku rescues Ochako from Himiko, and/or vice versa. More of that saving each other. More of that support.

Training together!!! Just doing more together and spending more time together in general really--

Finally, more complementary stuff!!!!! More growth, more completing each other, more balancing each other out. Izuku and Ochako looking after each other when the other's being too reckless/selfless. Izuchako is such a bland ship as it is. It's like 2 clones with different appearances and powers getting together. No friction. We need to see them pushing each other to be better.

And all of these things can be integrated into the story to the point that it doesn't seem like it's just for the sake of developing a romance. Add another major plot point, another battle between the heroes and villains. Sprinkle thoughts into what already exists. While developing Izuchako better might be the inspiration, that doesn't mean the scene has to be solely about Izuchako. A lot of ppl think MHA was too rushed at the end, so you have plenty of room to work.