How much do editors care about author affiliations and previous publications in the field?
In principle your background and affiliation should play no role, and the manuscript will be handled and reviewed on its merits only. Now, in practice, editors are only human, and may subconciously show some bias against unknown authors, and may deal with the paper with more skepticism than usual. However I do believe that most editors are professional enough to give the manuscript a fair evaluation.

Of course the very top journals are very selective, so that even for well-known authors in the field it is difficult to get published there. Especially if you are new to a field, it might be a good idea to first get feedback on your manuscript from someone who is more familiar with the field, to avoid disappointment.