I like this being the hub for the Threat battles. Good plan.

Could we just do both? have a Canon-1 Threat where they just take over one planet, and then do Canon-Threat where the Threat is capable of 
spreading to other planets?

Like, we could have the War for Oryu, and for Canon-1, that'll be the end of it. No one goes to Oryu anymore except for some unlucky protagonists. And then, maybe at some point in time if people are interested, we could do a Canon-Threat with some other people where it has the capability to evolve and attack other planets.

But right now, let's just do Oryu.

So, for clarity sake, this IS taking place before a majority of the Andreemea stories? So it's the UNT in the height of it's power, but since it's in the past, the technology is weaker... Okay, sounds good. By the time the other stories come around, the Threat will have taken over the entire planet so even orbital bombardments couldn't uproot it. It'd be like bombing the planets surface. No point, really.

It's pretty easy to come up with some characters that will only be used for one RP and will probably die or something. I don't think you really need to plan out some 2d characters until you flesh them out later.

Okay, so, what should the Threat look like in detail?

100 feet tall, big mushy wormy head, a hivemind of different organisms working together with fungus and plants covering it that shoot acid-poison. Also, since it's so big, it has different animals living inside it that assist in it it's conquest. It's hands are just three big fingers that grab and smash, and they fall down to the bottom of his knees. It's feet are... I dunno. What should it's feet look like?