I’m surprised to hear that you can’t successfully deploy the 700Mbyte. Is that failing? Submodules is likely to be a bit of a pain in the tuckus, requiring our help to manipulate deploy keys every time you create a new one. Not sure about subtrees, but I doubt that it would be any better.
If you can’t deploy, I’d start with a “what happens when you try, and please link to the build logs?” response, and assuming that there is some blocking factor that is really around size, I’d instead suggest a few pieces, stitched together like this:
…since you can self-serve on that and thus it can scale easily 