How did the myth of Jesus' resurrection originate?

[Aractus]

The fact that the accounts are similar on many of the main points yet vary on the details does not, to me, strike me as out of the ordinary for the circumstances described.

Yes I think on that point most of us would agree. I would just add to that "not out of the ordinary for separate testimonies".

The event that they describe is the issue, and if we were to consider it for any other person than Jesus, it wouldn't be too difficult to come up with a plausible explanation that does not involve a resurrection or the appearance of supernatural beings.

What we have as written record, I believe written from c. 45-48 AD (which is just a couple of years from the event), but regardless of when the records are written - even if Mark is written in 55 AD or 65 AD, it doesn't change the fact that what we have in the gospels is an early narrative that goes right back to the contemporary accounts. Even more so if you're willing to say that John the Apostle penned his own Gospel (that'd be first hand and why his account is more different than the others).

I think too much is made of the discrepancies in the details of a group of stories whose most critical points are made third-hand and from memories of events that are at least more than a decade past. It is pretty easy to piece together a more plausible story from what is written. Nor is it difficult to imagine motivations for inventing such a story.

Yes there could be motivations for inventing such a story, however one has to ask the question if it was invented then why didn't the Romans simply produce the rotting corpse to thwart the early Christian movement? The problem if it was invented is that it'd leave some trace - either the Romans would have had the body or the disciples would have had it, or the Jews - somebody had to have the body, if it was not in the tomb, so who had it?

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John, of course, has the weakest case mainly due to the duration of time between the events and his writing putting him generations away from the action. He further doesn't help his case by citing a fishing story (surely the weakest miracle ever described) in his, unique to him version.

That's an assumption. As I've discussed John could have been written as early as 55 AD assuming that Peter had already died by that time, and certainly doesn't have to be written later than 70AD (it doesn't even contain anything to do with the prophecy of the siege of Jerusalem). We do not know exactly when it's written, but it's pretty clear to anyone that it was written by the apostle John, making it an eyewitness account and therefore a trustworthy source.