hmmm.. idk.. i would think it would be better to generate a "parent", small modpack zip, containing your README, and any unique files to the modpack... and have some way of creating a list of URLs for the included mods, which point to the appropriate version/package of each mod, that is *already* hosted on SD...
then when the user wants to download the modpack, the small "parent" zip container is opened, and the mods requested are pulled down, and packaged in this "parent" zip, and shipped...
is this what is planned?
also, theres the matter of updated mods... if you create these huge packs, and keep them, i am sure they will quickly get outdated... it could be a *single*, included tiny plugin mod, that makes a whole several-GBs sized .zip worthless