Hmm, does the whole "order" thing work with lore? Im no loremaster, but it seems like a large thing to add on to an already established piece of the TES universe. Since there will undoutably be an Imperial Legion in OB, just not in a joinable form, im guessing any faction mod for it will probably have to conform to what is already there. Same would go for an Imperial Cult mod.
Oh, and most of what I said in my Imperial Cult thread would apply here, since its the same basic concept exept Legion instead of Cult

. Therefore I strongly suggest you try and seek out other people planning to mod this, so we don't end up with duplicates.