Pseudonymous publication of a series of texts online when a bad guy is expected to join in with fakes: will this approach to PGP verifiability work?
Yes, properly implemented including choice of keys and parameters, what's proposed makes Bob detectable when publishing texts under the pseudonymous identity used by Alice in stage A.

One detail is not made explicit: in step A2 the "signature made using her PGP private key" must be a (detached) signature of at least the text in A1. It is not useful to include in what's signed the PGP public key and fingerprint; but as long as it remains easy to verify the signature and extract the public key and fingerprint, such inclusion does not harm.

In stage B, Alice should I believe try to keep the same signing habits as in stage A, still including her PGP public key and fingerprint, and signing the same elements as she did in stage A. Things still work if the public key is removed (like due to limited publishing space), but including it eases the work of whoever actually try to sort out things, and makes it easier to detect forgeries when Bob chooses the first or second of these strategies:


not including a public key in his messages
including his public key in his messages
including Alice's public key in his messages


Per common practice, the date carried in Alice's signatures should be shortly before the date of the usenet posts or publication; anything else will raise suspicion.