This is the way I went a few years ago. You may want to borrow an idea or two - or not.
WBB 027 FA2's. AA. I added Alco sound, ERR Cruise Commander (can motors required), an Electrocoupler at each end, directional headlights, and I moved one powered truck to the dummy, so both are powered. Not needed; I just liked the idea. Big upgrade for a little locomotive, but it's a jewel. Fantastic switcher.
Added side numbers. Always loved the Erie scheme, but it no longer says "Erie".
My "tether" - isn't. I have to pick these up together, but they are easy to handle. One day, a diaphragm will hide the wires.