I want to ask you a question. (Direct, possibly too direct in some cases) I’ve been wanting to ask you a question. (For some time) I wanted to ask you a question. (Softer) I was wanting to ask you a question. (More casual) Very similar meanings, slightly different nuance.

Yep! You can also say, "I wanted to ask you a question." Both work :)

Yes.

Just an observation: It seems like British English speakers approve it but American English speakers think it is ungrammatical or at least weird. https://ell.stackexchange.com/questions/191669/is-i-was-wanting-to-know-grammatically-correct It is interesting because generally British English speakers are the naysayers :) We learned that stative emotion verbs (like want) aren't used in continuous tenses at school. https://www.perfect-english-grammar.com/stative-verbs.html

Yes.