My errand bike was stored outside for over a decade before I bought it for $5 USD. When I got all the parts off of the frame, I applied a good coat of Frame Saver inside the frame because I planned to store it outside in the future.
https://www.amazon.com/Weigles-Bicyc.../dp/B0012GO58Y
I got my can of Frame Saver at the local bike shop, Amazon is out. I am not familiar with the Pro Gold version of it, but that might be a good alternative.
Before you buy new brakes, maybe new cables will solve the friction issue.
You can buy a quill stem or you can buy a quill to threadless adapter that allows you to use a threadless stem.
https://velo-orange.com/collections/stems
I think that Velo Orange might make the tallest adapter, not sure who would have the tallest quill stem.
A good cable cutter is not cheap, but it makes life so much easier when you are changing cables. Shifter outer housing is almost impossible to cut without a bike cable cutter. That might be the most expensive single bike tool that a lot of home mechanics buy. Mine is a Sram, bought it from a local store. Of all my bike tools I think it is the most expensive single item I bought.