Hello @Hannah11,
have you tried timeline view already to allow you to better visualize dependencies and more?
Your suggestion with subtasks is what I would probably go for otherwise, yes you have to expand them to see all but then you can clearly see what belongs where
Otherwise have you ever tried using the board view? Then you have all the task that belong together and the milestone in one column?
Or adding tags or custom fields might help? As then you can easily also filter to view only tasks that have a specific tag added or entry in the custom field.
Oh and also have a look here - point F13 - 🔥 Hottest feature requests and their workarounds
Not sure if that helps?