it looks like a good design to me just missing fiber glass. no solder joints seems nice
you could clean them in a ultrasonic cleaner with copper safe cleaning solution (important). obviously try on one.
for something like that probobly re-ultrasonic cleaner it for a few seconds in DI water, then rinse with fresh DI water from a squirter, blow dry as much as possible and then let it dry in a chamber with desiccant (non corrosive, like the clay kind). I noticed if you just throw them in the oven sometimes it tarnishes a bit randomly
with regular cleaners I saw some metals rapidly tarnish.
short duration. I recommend you pull the dirtier ones for more control
dielectric grease will be good. from the sound of things silicone based anything will be fine with the plastic. the danger is using a grease that can damage the plastic.
I recommend doing it on one piece to make sure its OK, then work in small batches. don't dump everything in anything unless you are really sure.
you might hear citric acid but be careful. I left something in the Ultrasonic cleaner for like 10 min with citric acid (it was not meant for this, I thought it was soap) and it actually started plating the wall of the cleaner ! don't ask me how, I assume it made a battery!
it is very much on duration. it will be clean enough in short order, its not a magical repolishing machine BTW. The copper looks nice because it was mechanically stamped or polished or some shit. you can get rid of the oxides but it won't look quite right unless its repolished. electropolishing if you wanna fuck with that, IMO hard.
the mistake you can do is over-do. a quick clean for 30 seconds should be enough.
but the maintake is do gradual experiments and there is no magic bullet (maybe plasmaelectrolytic polishing is, but good luck with that setup! normal electropolishing is not that hard compared to plasma version). there is also electrocleaning, which is different then electropolishing. all the electro process are hard to execute compared to a quick ultrasonic dip BTW. I have some threads on electrocleaning and polishing (the brush process though is different and that is for nasty ass weld stuff). I consider it fun and even did a quick electroclean of a VNA test fixture before lol, but that shit is very technical. the problem is often that you don't have uniform field. with plasma you do but complex geometries = harder to electroanything. you are talking masking etc
just renember very good rinsing and soaking etc in distilled deionized water at the end unless you want spots to appear when dry when working with copper and chemicals! tap water can make it go off.