I'd like to share some of the popular opinion driving these relationship descriptions.
Michishige ⇔ Fukumura: Lolicon comrades
We knew Sayu was a lolicon for Riho, but for Fukuchan it's a little harder to detect for most people who aren't paying her much attention.
She's nowhere near as vocal about it as Sayu and tends not to say controversial things Sayu says. (Like publicly stating a desire to abduct Riho.)
She has said though, that she likes cute girls, especially those of elementary school age.
Also, she has stated on the radio that she has something of a fang-fetish, and likes Masaki's teeth. (It's slight, but sometimes detectable.)
Directly after saying this, she tried to get Zukki to admit having fangs too. (Zukki denied this, which I think disappointed Fukuchan a little. lol)
Her lolicon image kind of got a boost from when one wota heard from her at an event that she is a fan of "Maria-sama ga Miteru".
That's a shojo manga (Fukuchan is a stated fan of the genre) & anime that features a girls-only Catholic school.
I understand this one has some yuri overtones, and Mizuki seems to have absorbed the caring older-sister/senpai role from this kind of manga.
Sayashi -> Fukumura, Ishida: Pervs over them
Riho has a skin fetish, and Fukuchan's skin is some of the best!
Sayu blogged about touching it and Reina even commented on it on HPT during the shooting for Only You.
Riho supposedly (I've never seen/heard a primary source on this) said during last year's Hawaii FC tour that she was surprised at how large Fukuchan's chest is.
Perhaps the most damning evidence is when Riho said for a concert's self-intro MC that she loves Fukuchan's... everything. (specifically mentioning her arms and calves)
This got quite a few "yada~" and "hentai!" reactions from the other girls.
For Ayumi, I've only heard Riho talk on the radio about being attracted to her lips. (and I think wanting to kiss them or something?)
Other than this, I can't think of much else here.
Fukumura, Ishida, Suzuki: AyuMiZukki (and so a new comedy trio was born)
Aside from seeing the three of them introduce themselves as this in one of the merchandise channel's youtube videos, there's evidence this goes deeper.
For Fukuchan <-> Kanon, the usual evidence that is brought up is the part during Bijo Gaku where Fukuchan is helping Zukki learn the dance for one of their first FC events.
Fukuchan praises Zukki's improvement, at which point Zukki goes, "It's because Mizuki-chan helped me." and hugs her. (See "Maria-sama ga Miteru" above)
For Ayumi and Zukki, they appear quite frequently in blog pictures together, and Ayumi was even wearing Zukki's green tour T-shirt in one of them.
There's a similar rate of blog photo co-appearances between Fukuchan and Ayumi as well, and the image is further strengthened by their both being the same grade in school.
The whole grouping gives me kind of a Three Stooges type of feeling, with regard to their roles in the group.
Fukuchan is the leader (Moe), Zukki is the lulzy one (Curly), and Ayumi is the react-er (Larry).
Michishige -> Sato: Pervs over her...slightly.
Popular speculation is that Sayu, being the lolicon she is, has her feelings for Riho fading a little due to Riho's physical growth.
I believe one listener on her radio show asked her about this and she said something about Riho becoming an exception to her normal preference to loving small things.
In any case, childish Masaki is the next logical target for Sayu's gaze.
Ishida ⇔ Kudo: Are good friends despite fighting a lot (Tom & Jerry relationship...lol)
A newer trend among the wotas seems to be pairing these two up as a de facto couple, with both of them being somewhat tsundere about it.
I think Kuduu's new haircut may also have something to do with this.
I do find it interesting that the Kuduu/Masaki pairing or SayaSuzu were not in there, especially since the Ponpon combi was mentioned.