Great work! I belive that you're not required to set numbers or rarity, i have done it with mine mostly to keep things tidy but i only made a handful of sets, for the whole lot it would require extra work that might be done after everything is properlly listed.
Which downloader are you refering to to get the images, a browser downloader? Austinio7116 posted
here a really neat script to get cards from scryfall it might come handy especially because it looks like it outputs in a file the card list of the set you are downloading (i haven't tried the script yet)
For plain and simple deck building using Deck Editor, I think that it's probaly easy to do it, there is only the need for another section to filter the cards by set for Promos instead of putting them in Other Sets. For quests there is a little more work to be done specifying rewards and whatnot but it's doable overtime i guess.