With my limited Redstone ability, I've come up with an Item Silo (Download the example world here) that behaves exactly as I want (more or less), and I've compacted it as much as I can based on my skill level. That said, I'm sure it could be compacted further, or that a more compact version already exists and I just don't know what I'm searching for >_<
The main features of my silo are that the user only ever interacts with the chest at the bottom, which when too full empties deeper into the silo until there is enough room for more to be put in the chest, or if too empty fills from the silo until there's a decent amount of whatever's stored available to the user. The design can be expanded vertically to increase capacity, and an indicator running up the front displays at a glace how stocked the silo is.
The only other thing I'd like to see changed is for the indicators to show when the chest they represent is full, rather than show when it has any amount of items inside, though I can live without.
Any help or advice is much appreciated, and thanks in advance to those that do!