Looking for some help here from someone that knows how to manipulate redstone well, I'm still very new to minecraft and the intricacies of how competitors and repeats and powering different things work is still above my head.

So I have an item sorter in my basement right now in survival mode, iron is still tight for me, so to upgrade from a standard item sorter to a multi item sorter by the designs I've seen aren't happening. Plus I want something that isn't as large as the ones I've seen.

Here is a link to the design I use now

https://youtu.be/bx4VULALtqE

So, my idea is combining how a minecart loader/unloader works with this design.
You would have the dump chest feed items into a minecart chest/hopper.
Eliminate the top row of hoppers
Let's say I want to sort 2 items into 1 chest, the now middle row would have 2 hoppers feeding down to the bottom row of hoppers, the bottom row of hoppers all feed forward to the sorted chest.
Now the rails you would snake along on top of that while middle row of hoppers.

The part I don't know if it's possible, or how to do, is there a way using the different rails available, to make the minecart stop when it goes over a hopper it has an item to dump into, unload that item, then continue forward to the next until it reaches the end of the line, then circles back around to pick up it's next load?

Also would there be a more compact way to power that middle row, as it would start to extend out pretty far the more items you need to sort to 1 chest.