I think the upshot here is that Apple needs to do a better job informing the user of the status of the update process, so we can determine whether the update has failed or not.
I sorted out my problems … which was a relief. But i wiped everything and started again. Drastic. and not without misgivings. but all was fine in the end … esp once I found software to help me run an old version of iTunes.
was advised that 3rd party software (in my case, an application to help me run my old scanner) had probably disrupted my installation. That said it does take a long time to download and gives no real indication of progress