That is one part of the question, definitely, but one poster already mentioned that deleting decks form quest mode alone isn't yet a feature. Considering this limitation at the moment, I would hope to simply remove cards from the entire game instead. I wouldn't think it would be too difficult, for example I see a couple of files and folders which lists the different sets such as blocks.txt or setdata.txt, or perhaps the Boosterdata folder. Deleting some of these files/folders or deleting some of the code in the txt files I would think would "trick" the game into thinking that those files/cards aren't available in the game. I just need to know which files or code to delete to remove any given set from the game. I suppose I would be doing the opposite of what you do when you add a new set or cards to the game.
Again, the purpose of this would be to potentially only allow say M12 cards only in the entire game, thus making Forge really only have around 300 cards or so, a much more manageable number for a newbie like myself

I do realize, however, that I can draft and booster deck from certain sets, but just not from quest mode or constructed.
Thanks for your time! I'm new to Forge and am loving it!