This particular machine's insides becomes less of a repair and more of a restoration. 😳
That means a lot of tedious, skilled work is required to keep it going far into the future.
However, If you repair the worst looking bits, and can get it working for now, that may be all you care to do. But, this stuff will most likely keep eating away at itself. 🙁
If this was something you wished to give the best chance of working in 10 years time, my recommendation is to clean as much of the green copper oxide as you can. You may even need to use a tiny wire brush on components on the Analog board. Removing each component one by one, cleaning and inspecting is likely necessary for longevity.
The solder side of the Analog board may even have blackened joints and tracks. This is where corrosion has already begun. Such joints really need to be cleaned back to copper and resoldered and re-coated. Some tracks may have been "eaten" through, causing an open circuit that needs to be bridged. Again, this is very tedious work.
For the Logic board, similar methods should be used. It will no doubt look worse than it does now after cleaning but that's where this machine's life has got to. Some tracks may need to be checked for open-circuits just like the analog board, the tracks can be effectively etched right through.
For the rusty metal chassis, I'd remove it and ask somebody with a sand-blaster to bring it back to near new condition.
Please note that I have NOT undertaken repairs such as this on a Mac 128/512/Plus, but this is how I would proceed. You need to find a balance between getting it to work and how much time and skill you can throw at it. Sadly, due to leaking clock batteries that's just how it is. 😳
