Again, the subjunctive is not needed here. Should be "Vinum rubrum volo."
Yes, but classical Latin does not use the subjunctive for politeness. Independent uses of the subjunctive are reserved for other functions: https://www.thelatinlibrary.com/101/Subjunctive1.pdf.
This link seems to list such a usage, but I can't find it anywhere else. https://classics.osu.edu/Undergraduate-Studies/Latin-Program/Grammar/mood/subjunctive/independent-subjunctive
Yes, there is a potential subjunctive, I'll agree. But I just don't know that I've ever encountered it being used that way. More like wishing for things that potentially could be true...ala "Would that it would rain today!" I don't know. I might be fighting an uphill battle here.