Positivism isn't necessarily true, and if it is, it still doesn't get you to 6, because LP recommends you have no metaphysics which would imply no solipsistic metaphysics. (LP might be compatible with the claim that your own sense-data are all you can know , but that isn't quite the same thing).
There's a soft patch around 5 and 6. Why is testability important? It's a charactersitic of science, but science assumes an external world. It's not a characteristic of philosophy -- good explanation is enough in philosophy, and the general posit of some sort of external world does explanatory work. And it's separate from the specific posit that the external world is knowable in some particular way.
There is the simple observation that one has no conscious experience during dreamless sleep. (A panpsychist could respond that maybe one merely lacks memory of one's sleeping experience, but that would be epicyclic).
That's just ordinary compatibilism -- as I said, "it’s not libertarian free will." All the work is being done by using a definition of free will that doesn't require indeterministic "elbow room", so none of it is being done by all the physics and metaphysics. If it is valid, it would be just as valid under naturalistic monism, supernaturalistic determinism, etc.
And compatibilism isn't universally accepted as the solution to free will because the quale of freedom is libertarian -- one feels that one could have done otherwise. (At least , mine is like that).
An additional non physical layer of consciousness might buy you qualia, but delivers no guarantee that they will be accurate... a quale of libertarian free will is necessarily illusory under determinism.
An additional non physical layer of consciousness might have bought you downwards causation and libertarian free will.
But you are not legitimising it as a subjective impression that correctly represents reality... only as an illusion: you can feel free in a deterministic world, but you can't be free in one.
Under physicalist epiphenomenalism (which is the standard approach to the mind-matter relation), the mind is super-impressed on reality, perfectly synchronized, and parallel to it.
Under dualist epiphenomenalism, that might be true. Physicalism has it either that consciousness is non existent rather than causally idle (eliminitavism), or identical to physical brain states (and therefore sharing their causal powers).
Understanding why some physical systems make an emergent consciousness appear (the so called “hard problem of consciousness”) or finding a procedure that quantify the intensity of consciousness emerging from a physical system (the so called “pretty hard” problem of consciousness) is impossible:
You could have given a reason why.
It's a warning if the history consists of various groups having extreme confidence about solving all the problems in ways that subsequent groups don't accept.
You are conflating subjective as in "by subjects" with subjective as in "for subjects". A subject can have preferences for objectivity, universality, impartiallity, etc.
The other problem is that MWI is up against various subjective and non-realist interpretations, so it's not it's not the case that you can build an ontological model of every interpretation.
"it" isn't a single theory.
The argument that Everettian MW is favoured by Solomonoff induction, is flawed.
If the program running the SWE outputs information about all worlds on a single output tape, they are going to have to be concatenated or interleaved somehow. Which means that to make use of the information, you gave to identify the subset of bits relating to your world. That's extra complexity which isn't accounted for because it's being done by hand, as it were..