This is something I've been thinking about for a long time.
My first goal would be to capture the mystery of the original line. I'd make sure all the marketing is vague imagery that captures the imagination of the public. Posters: A canister washed up on a golden beach. A strange hive-like structure shrouded in a green mist. A seemingly ancient carving of a mask (Hau) into dark, mossy rock. Only thing to go on would be the one unifying word - Bionicle. These would be the early phase marketing posters, before details of the film start being revealed, just as a hook. Some will recognise the name and know what's going on, some won't, the only objective here is just to recapture that mystery.
Marketing phase 2: ARG. My favourite idea so far is to build 6 life size toa canisters, and place them on beaches around the world - get social media talking. This is the imagery you want people to remember, have the canisters make people think "oh, that's bionicle" - same way Harry Potter has the 'lightning' scar, and Star Wars have the Imperial Star Destroyers. That's what set the toys apart back in the day and that's what will set the films apart now.
Then obviously you have the teasers, trailers, movie posters where you start to reveal the plot a little more.
Film itself? The Lego Movie shows that you can make a fully animated movie look realistic, so we go that route utilizing motion capture to make the movement feel real - akin to Ceasar in Planet of the Apes or Ultron. Obviously story-wise, we start with 2001, focus on the Toa, but of all the Matoran you want to be focusing on Matoro - have him be the character people can relate to.
Regarding sequels, 02, 03, skip Metru Nui (this will be brought up later) - probably skim over the Bohrok Kal and have the third film just be Mask of Light. Instead use the Bohrok Kal as generals of the Bohrok in 02, answering only to the Bahrag - this is a departure but you still want to give fans the Kal even if it is in a new context. Throughout these sequels, make sure to keep giving a good amount of screen time to Matoro and progressively start introducing the soon-to-be Inika as his friends. Have them be pivotal to helping the Toa defeat Makuta when you get to the Mask of Light storyline.
These first three films should all have a consistent feel - I suggest the soundtrack should be composed all by the same person: Mick Gordon. Listen to his work on killer instinct, he knows how to merge genres. It should sound tribal at it's core (focus on drums), with electronic / rock when the action kicks in to give it that extra punch.
With the initial trilogy done we move onto the Ignition trilogy where we make Matoro the main character. We've already set him and his friends up, the audience have seen them develop into braver characters so it's not going to be jarring with a new set of Toa. With this new trilogy you want to be changing things up; audiences are familiar with what Bionicle is and now you want to start really playing up the darker tone 06 introduced. Start the film with the Toa Nuva being defeated, let them know the Piraka mean business.
Another thing to change up is the soundtrack. Yes, one composer can be versatile but you want a fresh take, so for Ignition you bring on Front Line Assembly. Listen to their songs Beneath The Rubble, Dopamine and Unleashed. These sound Bionicle to me, and the high intensity heavy industrial rock will match the literally universe ending stakes.
We all know what happens, Mata Nui Awakens, yadda yadda. End the film series with the Bara Magna saga and a battle between Mata Nui and Makuta of epic proportions. Every punch sending earthquakes across the planet. This is the storyline I've thought least about, perhaps bring Mick Gordon back for the soundtrack to capture some of that nostalgia for the first three films and bring it full circle.
Then... finished... or is it? We still have the Metru Nui saga to cover and tonnes of other material that could be adapted - introducing BIONICLE Legends; a series of stories set throughout the Bionicle saga akin to the Star Wars spin-offs. Here you can have single one-off movies or tell a story across multiple like the Toa Metru / Hordika storyline. Yeah, I got ahead of myself with this, very few franchises have the luxury of this many follow-ups, but it's fun to think about.
Now, casting; the only casting I'm dead set on is Jeremy Irons as Turaga Vakama. I think he would really sell this former Toa, who deep down still yearns for that adventure.
Sorry, this was a lot of words and I probably made an unholy amount of typos and sentences that make no sense. I wrote this in a frenzy of "OMG I CAN FINALLY TALK ABOUT THIS".
EDIT: Forgot to mention one thing: first thing I'd do is bring on Farshtey and Faber as producers and story advisers - making a Bionicle movie without them involved would be blasphemy.