Very intelligent assumption. The outcomes can be interesting because by grafting research ideas the way you have done, one can open up new vistas not conceived before.

Without a doubt, of course you can do it. The analysis presented by both authors is similar and does not contradict each other in their discipline. What you should keep in mind is that the epistemological basis of each author is different so your theoretical discussion should raise it and you will have to see or find where the coincidences are. This will be fundamental to give support to the methodology used.

you can be as creative as you can when you triangulate two pr more theoretical frameworks. Most importantly, you try to provide a logical justification for that.

Oke ..

I think so since Fairclough's CDA wanted to disclose latent meanings of the texts, we also may use some kind of other explanation provided by semiotics such as Barthes' work to combine with.