Hmmm, load centers. Well i usually install SqD because of value and availabilty in breakers for avg homeowners.
They are a good "builders grade" panel. Eventually when i upgrade my own service, im gonna get
The SqD with copper bus. Sure its a bit more, but with Cu there is less to worry about with heat and friction.
I like to put NoAl-ox on the non-Cu panels before installing breakers. It cuts down on friction and scratching
of the bars which could lead to arcing on the breakers.
As for your switch dilemma, it looks as tho you have a decent understanding.
If you know how to trace wires with continuity, that should help sort them out.
When you disassemble all switch box wiring, cap all the wires separately and check which gets power from the panel.
After that, labeling all the travelers and feeds will get you on your way
You can check continuity by nutting wires together, but this could be time consuming.
I like to use a remote continuity tester. You can pick one up at Lowes for around $20, and it can save you time.