As far as understanding archetypes and tropes, Akiba does not fit into the role of the villain, at least not for now. Rika is the one who fits in this part( villain being the opposite of the hero, creating obstacles and difficulties for the hero).
1 - True, but that can be attributted to other reasons for later.
2 - True, and she started bonding with him. However, views from both of them differ. Akiba wants, at least, an emotional affair with Sousuke.
3 - Not really obsessed, she is sexually frustrated( chapters 2 through 4 explains this). Later on she switches full time with an obsession for Sousuke;
4 - More complicated issue, overall. She doesn't know how deep this whole things go( she saw it a lot of times with various different couples), and who it could damage( families and kids). Besides, if someone discovered it was her, they could go for a revenge.
5 - She did so because of her obsession with Sousuke. Sacrificing herself and all show us more of an emotional depedancy.
6 - Already been pointed out. It could be different things, including herself dealing with what Sousuke will do and( a conjecture) even she being blackmailed by Rika again.
7 - True. I'd even go for obsessed. But him being married, at this point, is amounting to less, since they have proof of the videos Rika did with Shingo.
8 - Really? When that happened? Kinda forgot this one.
As of now, unless the story pull an idiotic excuse( like "it wasn't her, we just made sure that the other person looked like her in minimum details level" and Shingo going with "I said they were my sex videos with her, but it wasn't her at all") we stay with the "facts" that it was Rika in the videos, she did it with Shingo, Shingo didn't deny, and now she's been on the run for 3 weeks.
It seems to me that you could explore this direction.
The idea of having three initially unrelated plotlines that gradually converge by the time of the trip looks interesting - at least that’s how I would have done it if I were the author.
I understand, of course, that the idea that follows would be rather far-fetched and not have much foundation, but still.
1) Rika’s content-production business
Rika works in organizing production, promotion, and producing content.
At the school where her daughter studies there are several people she is involved with in business.
The first is Shiratori. Thanks to Shiratori’s mentoring, Rika achieves good profitability in her business, plus gains access to recommendations that can help her daughter’s future prospects.
The second is Shingo Mori. Through collaborating with him, she gets an opportunity to expand her field of activity, use different filming techniques, and work with various actresses.
As for why Rika chooses him in particular, I would pick this reason: his attractive appearance, which helps him successfully lure other women into this work.
And we already have an example where he practiced this with another woman.
The third is a freelancer whom she lends money to, earning additionally for the development of her business.
2) Shingo Mori’s arc
After meeting Rika, he achieves incredible success in his business, and he constantly has sex with various women.
Rika becomes for him an unattainable ideal - intellectually and in age she is above him.
Even while filming with other women, he never manages to get what he truly wants now: sex with Rika.
So he decides to involve a third person and make her look as close to Rika as possible - the choice falls on the teacher, Megumi.
(Although this part is optional.)
Unexpectedly for him, the new actress begins to bring in quite a good income.
He keeps the best take on an SD card, completely uncensored, for regular self-gratification.
3) The arc of teacher Akiba
Falling under Shingo Mori’s influence, she remains unsatisfied.
Sexually frustrated and clearly mentally unstable, she finds a new outlet for herself: setting up hidden cameras in a school filled with debauchery.
(She installed hidden cameras at the sports festival and recorded Rika and Shiratori’s conversation, so she has both the cameras and experience using them.)
At the time of the manga’s events, she accidentally meets Sosuke - the husband of the woman whose image she has to imitate.
Sosuke is investigating his wife’s infidelity.
Akiba decides that she can finally experience real pleasure if she inserts herself into the situation through Sosuke and exerts influence over Rika’s business and the whole corrupt atmosphere at the school - filming everything and posting text messages in a degrading tone to surpass Rika’s content in popularity.
As the story progresses, Akiba fills the content she releases with sharp, juicy details.
She takes away Shiratori’s ability to give recommendations and appropriates this influence for herself.
One can even imagine that Terauchi’s constant offers to Sosuke at work are directly tied to Akiba’s channel.
4) Regarding Rika’s escape
When returning the SD card, Rika realizes that Sosuke really has been monitoring her actions - something she had not suspected.
Before this, after returning the SD card, Shingo Mori uploaded the bar video.
Meeting Shingo in the corridor and checking the SD card to see what her husband might have been able to view, she discovers that among the original files are images of Shingo kissing someone with a face resembling hers.
She deletes all content connected to herself.
For the rest of the evening, she tries to get Sosuke to talk, but failing that, she stays in the room and waits for him.
At the moment Shingo is defeated, Akiba leaves the location and heads to Rika.
Everything unfolds before Rika in such a way that explaining the situation to Sosuke becomes impossible.
Rika makes an impulsive escape.
All these directions are extremely tentative, but I would really like to see three plotlines that remain not fully connected and each plays its own game.
Within this setup, Sosuke’s story looks like a small boat in a raging sea of truly significant events.
And that would be genuinely interesting, I think.
It would be a real shame if everything ends up being reduced to the banal “one character - Rika - is the villain.”