I don’t think the lifetime of the drive would be affected though — writing to solid state memory involves no mechanical parts so that shouldn’t be a problem.

Re: a) — good point about the URL, it would make sense if Zotero saved it in this case. This is something that should be suggested in the Zotero forums. In fact, I just did it.
Re: b), Zotero uses ‘translators’ to grab metadata from sites. Every site needs its own custom-built translator, so only if the sites you’re alluding to are very common it would pay off to develop one (see scaffold).
Re c), as a rule, you need separate items for separate citations. In that case something like ‘book section’ comes closest to what you describe, and you could quickly generate items for all sections using the duplicating strategy described in tip #2. First add the containing item, then duplicate it once, make the duplicate into a book section, and specify that it is related to the container. If you now duplicate this duplicate, all of them will be conveniently linked to the container item.

In short, there are no automated solutions for b) and c) due to the fact there is no generic way for Zotero to sniff out bibliographic details, since every site is structured differently. In the future, some cb2bib implementation may help.

Tried the first tip and Zotero created an attachment that was stored on disk (expected). The import however did not fill the source of the file into the URL field of the reference (unexpected)and there is no way of dragging-and-dropping it, or cutting-and-pasting the link attached to the PDF attachment into this field – You need to go back to the original site and find the URL again and extract it from the browser.

For my option b) above, I was alluding to sites where the metadata and PDF are on the same page. Is their a way of getting the metadata stored and PDF attached, with the URL to the PDF stored in the URL field of the item – with just one button or keystroke.

For my option c) above, by attaching multiple PDFs this creates a virtual library but how do you present this in a bibliography? My references need to provide both functions – a reference for me and a citation for my clients/readers.

for (a) I would use the first tip. For (b), I’m assuming you mean that the metadata is not ‘grabbable’ by Zotero; in that case you’d have to add it by hand (or try Google Scholar to find it in grabbable format somewhere else), after which you can drag the PDF onto it as in (a).
For c), simply save a snapshot of the overview and then attach the PDFs. In this case it pays off to rename them (00-contents, 01-chapter1, …, 11-appendix) so that they will be neatly ordered in Zotero.
For (d), attach all versions and take note of the version number either in the file name or in the note field available in the right pane when the file is selected. Or if you intend to cite the different versions, make duplicates and provide the dates of the versions to keep them apart.