Download the folders/zips separately. If you download everything at once, it will probably be a bit too heavy for DropBox to reliably send the files to you. Plus, there are versions with only presupported models or without any presupported models. So if you download everything at once you're doubling up on everything.
You will be able to redeem the files on MyMiniFactory early next month.
I'll also be sending out e-mails to redeem on MyMiniFactory soon. If you joined at a later date than when this came out. I don't have a schedule for updating the MyMiniFactory user group, but you will for sure get an e-mail early next month as stated above.