- About Tarantulas
Personal observation here (as a guy who had nothing to do with the mold choice on this one).
Transmetal Tarantulas was... well he was a bit like Bruce Lee. He wasn't bulky, but the guy was trim and toned (look at those abs!). And then he had a ginormous linebacker's shoulder pads thrown on, giving him an extremely wide chest and shoulders.
From the day Rook was revealed, that's kind of how I saw him too. His upper legs aren't all that bulky, and with the bomb disposal claw defining his job, I can interpret him as a moderate-sized guy inside of massively oversized protective shielding. And with this being Tarantulas working with the Predacon Secret before/instead of on ancient Earth getting turned into a spider, I can catch some interesting story vibes of him putting on some riot gear or a bomb disposal suit for a particularly tricky assignment.
As for the size of the head, thanks for pointing that out. But there has been a 3D printing made and correctly fitted to the body, even if the digital color/paint mock-up might appear to show something different.
- About the decision to use these versions of the characters and these alt modes.
The decision to make a Beast Wars Anniversary set came, well, years ago. However, since there is a very limited catalog of beast molds accessible (unless you go back to the original 20 year old molds... which does have some appeal, don't get me wrong) and since there was no knowledge of what Hasbro or Takara Tomy might do (again, we're talking a couple years ago) the focus has pretty much always been on making vehicular forms for the BW cast.
As far as how the Beast Wars Combiner Wars came about, I can't get too much into that. However I will say that Hasbro were very much excited by the concept of Fun Pub using current molds and branding to make the toy line and exclusives more cohesive.
So then with Combiner Wars in mind, Tripredacus seemed the most compelling choice for Beast Wars. Two Deluxe beasts and a Mega beast forming one of the first combiners since G1 getting turned into two Deluxe vehicles and a Voyager. And then to finish off the team of 5, Ravage and Tarantulas fit that theme quite well as being agents of the Council in the show.
The decision of show versus toys... well the Tripredacus toys already exist. And quite honestly they still hold up quite well 20 years later. The show models, however, have never had any sort of physical representation, so it became incredibly tempting to give them one finally. (Not to mention the show models where non-beasts, so that was an interesting point as well.)
Lastly, having seen and held the 3D printed heads, and seeing all of the design work and digital sculpts that led up to them, I think they fit the bodies much better than the mock-ups make it seem. I think that once samples start rolling in, some minds might be changed.
- About choice of colour, what impact Combiner Wars had, prices and souvenir figures.
The Tripredacus Council are red, silver, and black while Ravage is black, silver, and red. So I don't think he stands out as much as some are expecting. And Predacus will pull some of Tarantulas' colors into the combined mode.
I'm not sure I would agree with the Combiner Wars molds being called a "roadbump". They affected the course of the design and concept process, sure, but their hurdle isn't any higher than any other repaints really.
For the rest of your post, all I can say about the souvenirs right now is that I'm quite excited about them. And that it's too early to talk costs just yet.
- All about what went into the colours chosen and how it represents the most show accurate scheme possible, according to the Transformers Club.
The lighting after the little red disc lights are ignited makes it fairly clear that they are red and silver. The red reflects brighter on them where the red lamps shine on them, but as has been pointed out they are red where the white lamp shines on them too.
My personal interpretation of the scene is that the trick of the light/light source cheat is actually the part where they appear solid gray. More than likely the animators wanted to make their reveal a little more dramatic and therefore cut the saturation to nil so that the characters could blend in with the shadows more. This is done quite a lot in live-action filming when a scene is shot in the day time but then edited to look like night time - the saturation is cut and a blue filter applied.
Then when the lamps are activated we get bright red characters against a blue backdrop. Very contrast-y, very dramatic.
That's actually a really good idea, those molds fit well. My one critique is that the lack of Beast Molds in CW makes an RID homage not totally possible. That being said I don't think anyone would care.
limbs for all of our spare torso's we bought, and now, ignoring the anniversary of a beloved series that salvaged the brand just so they could cram more gimmick-laden G1 crap down our throats 
