C. Any tips for bleaching a dark water stain out of one of the veneer surfaces it if doesn't come out with sanding?
Yes, oxalic acid will remove staining. I say 'staining' because it may not remove all the discoloration. I had an AR2 cabinet with a pretty serious stain, and I was able to get most of it out.
It's available as crystals (I had to order it online), or in many deck cleaning solutions, which is likely available locally.