I am mostly interested in which approach you intended on.
I am not sure of the coding involved. However if it was not too difficult. I think it would be kind of cool to be able to pick what result you got from the usually available distribution possibilities. Basically pick your randomize dice roll but not a full custom breakdown. Probably be easier to code that then trying to make a balanced custom breakdown anyway.
For example two of the options for the two fate dice are ++ which is 2 cases, 6 foes, no obstacles, and 4 advantages or -- which is 3 of each type of card. Probably be easier to code pick the dice then the player having the option to do something like I want 4 cases, 4 Foes, no Obstacles, and 4 Advantages.
Sounds like you intend on just having the random dice rolled, having the game assemble the deck out of the right breakdown of cards for that dice roll and get them laid out. Which is good enough. Although if you wanted more input I would suggest having an option to reshuffle the card layout but not change the card type breakdown and/or any of the cards.