Serinox

Or he just already knew who Masumi was and that she is the sister of Akai because he has been working with Akai for a longer time now.

No, it wasn't. Haibara says in her introduction that she never intended to make a poison and that the untraceable killing was a side effect; and she also said she detest it being used as a poison.

You haven't gotten there yet, but there is a later point in the series where we get a case with extensive inner monologue/thoughts from Kogoro and nope, he straight up says there in thoughts that he has no idea why it happens, why he feels a stinging sensation before passing out, that he can really never remember anything and that he just accepts it because it works for him. That's the case that disproved any theory that Kogoro could be the Boss or BO for me, since he can fake his dialogue/reactions etc., but faking the inner thoughts would be massive cheating from Gosho (yeah, yeah, multiple personality disorder, schizophrenic etc, but Kogoro has never shown signs of something remotely like that, so just pulling that out of nowhere would still be cheating imo) and think of him what you want, he wouldn't go to such methods to fool the reader á la David Cage.

Episode 759, Conan sees her in the crowd at the hotel, plus with the photo Masumi showed him at the end of the Red Woman case, he assumes that she is living in Masumi's room. He also (unsuccessfully) bugs her room at the end of Episode 760.

More and more air-time? She appeared in 3 chapters in the last 100 chapters, Vermouth was disguised as her in more chapters (4) than she really appeared, so I wouldn't say she is getting more time in the manga than before. And I doubt appearing in M20 means anything, it wasn't even her first movie appearance.

But Eisuke's clumsiness wasn't a hoax entirely, he pretended to be naive and less smart than he actually was and he always tried to act inconspicuous and yes, he some of his accidents were faked, but his overall clumsiness was real.

If you look closely, she has her eyes closed when she does her bow and hits her head on the desk, so it's probably just she bowed too far because she was nervous. The last two DB cases gave us serious plot moments (Conan noticing the similarities between the MG and Haibara, Haibara revealing that Koji Haneda was on the APTX victim list) and there have been DB with serious plot moments in the past (The entire Detective Boys vs. Robber Group case where Scar Akai was introduced for example), so I wouldn't rule it out that something relating to the main plot happens in the next two files of this case.

Why would they meet though? Ai is purposely avoiding him because she still thinks he is a BO agent.

New one for File 959 (14.05.2016) Translation according to Shelury: Speaking of Nue, it reminds me of Studio Nue...

That's Movie 2 "The Fourteenth Target"

It was never confirmed that those were meant to be them, so you can't say that with certainty. Gosho said they are some of Akai's random FBI goons, so that's that.

Again, we see that Ai is enjoying her life. Also, did you hate your father when you were 18? Agasa is not really that old, he is just 52, still far from retirement age (and only one year older than Sonoko's father). Also (again), she didn't have a childhood, she didn't have friends when she was 7, she is getting a chance to relive the life she never had and she is shown to enjoy it.

Chapters 906-908, the case with the three first discoverers.

The side notes and the text on the cover pages are written by the editors though, not Gosho iirc, but even so, it would be a bit weird to refer to Kogoro in this manner, especially since he just had one of his nowadays rare Sleeping Kogoro appearances in 953.

Still better than calling Subaru and Scotch lolicons imo

It may be, but it says famous detective, so it would be a bit weird to do a flashback to when he wasn't famous at all yet. So no, I don't mean that flashback and I honestly don't really think it will even be Shinichi who the side note means, I'm realistic enough for that (but I can still hope, right?). Well, heart says yes and brain says no ^^

Could also be another flashback case with Shinichi, that would still technically be an appearance ^^

No, Shiho is two years older than him, with 18 she's already pretty much out of high school age in Japan. And again, she never had a childhood, so there's no reason for her not enjoy her reliving that time.

According to one of the veteran translators on DCTP, the Japanese police are required to take handwriting samples from everyone at the crime scene in some circumstances, because otherwise the case would get smashed down in court by lawyers, so I wouldn't read too much into it. Probably also just a plot device to make Bourbon see Okiya write with his left hand.

Kuroda's sudden aging? His hair became white because of the stress of the incident that put him into a coma, he didn't age rapidly or something.

Uh, no, he said that out loud. Those are speech bubbles on the page and not thought bubbles.

I hope for the same, but how would this make that happen? Ran already knows that she, Conan, Haibara and Jodie were involved with a crime back then. Even if she'd remember the face of the kidnapper, what would that accomplish? How would that get her involved in the whole BO business?

He doesn't know, as Gosho stated in a recent postcard that he might learn about that soon (probably during the resolution of this case)

Perhaps you missed it, but that was translated over on DCTP: