First, idiomatic Redux encourages you to “normalize” your state and flatten it as much as possible. Use objects keyed by item IDs to allow direct lookups of items, use arrays of IDs to denote ordering, and anywhere that one item needs to refer to another, it only stores the ID of the other item instead of the actual data. That allows you to do simpler lookups and updates of nested objects. See the Redux FAQ question on nested data.
Also, it looks like you’re currently storing a number of functions directly in your Redux state. Technically that works, but it’s definitely not idiomatic, and will break features like time-travel debugging, so it’s heavily discouraged. The Redux FAQ gives some more info on why storing non-serializable values in your Redux state is a bad idea.
edit:
As a follow-up, I recently added a new section to the Redux docs, on the topic of “Structuring Reducers”. In particular, this section includes chapters on “Normalizing State Shape” and “Updating Normalized Data”, as well as “Immutable Update Patterns”.