As regards 4, I'd say that while there may theoretically be arbitrarily powerful agents in math-space that are non-reflective, it's not clear that this is a pragmatic truth about most of the AIs that would exist in the long run - although we might be able to get very powerful non-reflective genies. So we're interested in some short-run solutions that involve nonreflectivity, but not long-run solutions.
I don't think 2 and 3 do have different answers. See the argument about what happens if you use an AI that only considers classical atomic hypotheses, in ontology_identification.html?lens=4657963068455733951
1 seems a bit odd. You could argue that the Argument from Mind Design Space Width supports it, but this just demonstrates that this initial argument may be too crude to do more than act as an intuition pump. By the time we're talking about the Argument from Reflective Stability, I don't think that argument supports "you can have circular preferences" any more. It's also not clear to me why 1 matters - all the arguments I know about, that depend on Orthogonality, still go through if we restrict ourselves to only agents with noncircular preferences. A friendly one should still exist, a paperclip maximizer should still exist.