Hi Jules,
Looks like you’re a natural at keeping things organized! I see your logic here, but unfortunately at this time subtasks cannot contain the master task info at the subtask level (assuming you’re talking about custom fields specifically). I recommend that instead of relying on subtasks for this purpose, you use sections and tasks at the project level. That said, you might be interested in the engaging debate about subtasks folks have had in the community here: To Subtask or not to Subtask
Let us know if you’d like us to workshop any of this with you. 