You can still write to floppies; the issue is that the newer OS versions don’t support writing to the HFS file system, which these floppies use. The other issue you would have is no USB drive can write to 800k floppies, just 1.4 MB ones.
As for cleaning and lubrication, I have a guide on YouTube:
You are right the PSU should work without (I didn't try it yet).
But it would be nice a) to know the values b) bring the PSU in the original status.
In general it would be nice to get more information about the PSU in Mac II for 110V and 220V countries.
By the way my PSU is for 220V ...