I wish to write a thesis that looks at how we can use sfl and appraisal theory in particular to analyse opinion columns and how these capture and expose identities as well as ideologies
Dear Tendai, I think first you should think of exact topic(s) in SFL which is in your main thrust areas of interests and specialties. Are you, for instance, interested in Grammatical Metaphor in SFL which is twofold: Ideational and interpersonal. In Appraisal theory, you can start by Attitudinal positioning. For more information, You can refer to my articles in Grammatical metaphor and appraisal framework in my profile. Hope these are helpful and informative.
I have written different papers on Appraisal Theory and newspaper discourse. You can have a look at my publications in my profile. They may be useful for your research.