I definitely agree with the notion that the marketing should be as ubiquitous as possible - not so much as to be annoying, but enough to make sure people know this is happening and exactly when; to make sure it doesn't slip under the radar. Also, finding a release slot when there isn't anything else big happening would be of vital importance, because otherwise it would probably stand zero chance. I love Bionicle, but let's be real here; outside of vague nostalgia and memes, it isn't really that big in the public eye.
Also important - go in with the possibility for sequels in mind, but don't plan on them from the outset; just announcing the idea of a 'cinematic universe' (even if it would be much more linear than most) would inherently generate a certain degree of antipathy toward the project, so go in with the intention of making something that will stand on its own merits first and foremost. Maybe you could have an aftercredits scene teasing Bohrok (since this would be an adaptation of 2001, best place to start is the beginning after all) or other future storylines, but even that feels like it would be pushing things too much.
But yeah, marketing. I do think going with the mystery angle to start off would be best, and let people know that this is going to be something new and unique that they wouldn't find anywhere else; but I feel relying solely on that would leave most people nonplussed or feeling it would be too 'weird' for them, so once we get to trailers and stuff, it would be better to show more. Not spoil the whole movie, of course, but give something more concrete for people to latch onto. I think the first like, 'teaser' trailer should focus on giving people a rundown of the premise - an abbreviated recap of the classic Legend Of Mata Nui and the Toa's arrival could work for that, establishing the stakes and conflict without giving anything away. After that, though, a second trailer should shift the focus onto the Toa themselves, and essentially sell them on the basis of their personalities and interpersonal conflict; kind of a 'how are these wildly disparate heroes possibly going to get along?' question.
And that conflict would then be a big focus of the actual script as well; for extra thematic resonance and general relatability, we could draw parallels between Mata Nui and Makuta's conflict as 'siblings' and the Toa, also considered brothers and sister, struggling to get along. I think framing it like that would kind of ground it in a more real-world sort of thing, even with the overall tribal and alien setting being compelling in its uniqueness. Unlike G2, we also want to give adequate time to worldbuilding and atmosphere, so having Takua's travels as a B-plot would help with that immersion as sort of a MNOG-lite. But the main intention would be to flesh out the Toa a little better, and make their path toward unity more of a plausible and compelling struggle as they hunt for the masks. At first they find their different approaches incompatible and think the others are doing it wrong, but over time they realize that those differences are their strength.
I'm thinking a four-act structure might make the most sense. The first act is all about the Toa's arrival and introductions, getting the Turaga's exposition, etc. and ending with their initial meeting, argument, and decision to split up. Second act would be their individual quests, with some time interacting with the Matoran as well; it would end in Lewa's infection and Onua's rescue, hammering in that they can't do this on their own. So in act three the Toa would reconvene and finish up the mask hunt in teams, and have to actually resolve or shelve their personality clashes in a meaningful way; this would end in a Triumph-Of-The-Toa-like scenario where Makuta goes all-out trying to destroy them or split them apart, but just winds up bringing them together more. Then the fourth act would be the actual descent into his lair, fighting the Manas, the Shadow Toa, and then Makuta himself, with the Shadow Toa encounter in particular providing final resolution to lingering issues with themselves and each other, and the Makuta encounter being essentially a test of that.
This... would probably be a bit of a longer film as a result; somewhere in the general vicinity of three hours. That could harm it in some ways, since less showing times in a day and all, but provided the marketing and timeslot are ideal, it shouldn't harm that end of things too much, and hopefully allow for a more complete artistic vision and better movie overall.
Also, since there's been a lot of discussion of music, my proposal would be someone like Bear McCreary for the score (since he's fairly versatile as a composer and his work on Battlestar Galactica has employed a lot of instruments and sounds from other parts of the world) with maybe some input from a techno musician like Daft Punk or Paul Oakenfold. I think the score would ideally be a fine mixture of techno, (in particular I'd think trance and drum'n'bass would play well with the alien tropical setting) traditional tribal, some mild symphonic elements, and hard rock, with a fair amount of variation and different balances of each as befitting each scene; ideally it would be the kind of soundtrack people could listen to and enjoy independently of the movie, instead of just fading into the background. New themes would be cool, but I think bringing back Nathan Furst's symphonic themes for MoL within the context of this mix of genres could be really cool too. A new Cryoshell song for the credits would be icing on the cake.
Aesthetics-wise, I think 'live-action' would do better, both for realizing it well and for getting people to take it seriously; for better or for worse animation isn't popular in the western sphere outside of children's content. (Which this would ideally be still oriented toward, no hard-R violence or whatever. Just, the idea is to have everyone like it, so attracting the adults and kids in equal measure is the aim?) Of course I say live action in quotes, but this would basically be motion-capture CGI paired with actual live-action shooting in various real-world locations, probably also somewhat accentuated with CG. As much practical stuff as possible, basically, to keep it feeling relatively authentic, even if ultimately a lot would still have to be done in post-production.
Also, for the designs I know some people really really insist they have to look like the sets, but I think something along the lines of the Miramax Trilogy would work better. Not the exact same style, mind you, but still in that general area, to allow for as much expressiveness and plausibility as possible. Mind you, it would be vital to avoid going full-on Bayformers with it, but like, a nice middle ground of detail vs comprehensibility would probably work. Think Bumblebee Movie but with more pistons and organic parts. (And since they don't have to transform, that would help out immensely; a lot of the detail would be more in like, giving them a plausible biology and articulation and expression, while still remaining faithful to the overall designs.)
And yeah, if, if it does well, then absolutely go for sequels, there's a lot of material to work from after all, and plenty of potential to actually improve on the original stuff instead of making a shallower imitation. Whether or not it'll stick with people is hard to say at this point, (also, if it would be theoretically coming out in the next five or so years, it risks having to compete with the Avatar sequels, which may dominate that niche of 'alien tropical settings' as far as novelty goes) but I think it could be done. The big thing would be to both make it new and unique and something people can't get anywhere else, while still making the characters relatable and compelling. And generally, just make sure people are aware of it at all to begin with.
I may have put like, completely way too much thought into this over the past few months.