Thanks for your reply vinnyvg.
I already "took the plunge", and obtained my EIN on Christmas Eve. To be honest, I have found the Apple Support Community threads very confusing on the matter, and made my decisions based on 2 blog posts recommended to me by fellow authors. I have listed them below, in case they can help anyone else too. As far as an IBAN number, I appear to already have one as routine on the top of my bank statements. (It appears to simply be a way to identify your bank account worldwide.)
2 very helpful blog posts:
http://catherineryanhoward.com/2012/02/24/non-us-self-publisher-tax-issues-dont- need-to-be-taxing/#comment-29944
http://lissowerbutts.com/getting-your-us-royalties-tax-back-non-american-authors -new-zealand-edition/
I am not qualified to give anyone tax or legal advice, but drew the following personal conclusions to my own nagging questions:
1. In an ideal world a personal ITIN would be required, but it is difficult to obtain, so an EIN will do.
2. To obtain an EIN you simply need to declare yourself a business, you do not need employees. In the UK this seems to be most easily achieved by declaring myself a "Sole Trader" business. The HMRC Tax Site provides info on this, and what it means. Current requirements seem to be that you register with them no later than October of your business' 2nd tax year, and send in annual UK self-assessment tax returns (presumably required for anyone selling ebooks anyway).
3. Naming your UK "Sole Trader" business using simply your real name with no additions seems to avoid having to carry out any further name-related checks (and possibly also avoids needing to produce stationery with your business name on?)
4. Becoming a business does not appear to effect my own house insurance, for now, as long as I only write ebooks as a hobby.
The 2 blogs above go step by step through the "how to get your EIN number" process.
I rang the IRS from the UK on 001 267 941 1099, selected new option 1 for foreign EINs, and got through instantly at 11am UK time. (7am Pennsylvania time. The friendly operator told me they were never usually busy that early in the morning. My earlier attempts to get through to that option in UK evenings had been unsuccessful, just getting an automated message to try another time. I think I may gave read somewhere that only so many foreign EINs now get given out each day, so wondered if the quota was already up by then? ) I went through my printed off SS4 form over the phone, and had my EIN in less than 10mins.
I was then instantly put through to a US tax lawyer, so that I could ask if annual tax returns were in fact required. His advice was simply that if I received a letter from the IRS requesting a tax return and I believed that I should be exempt, then it was very important that I immediately wrote back explaining why I believed I was exempt, and did not simply ignore the letter. I guess if my exemption reasons are incorrect under current tax laws, then at least that means the IRS will be back in touch explaining this.
The first blog post I mention above has a lengthy thread associated with it, and highlights one contributor's reasons as to why I could well find myself exempt from sending in annual US tax returns. I find the exact legal wording complex, however, and am left confused over whether the 3 exemption clauses are filled when doing business with Apple rather than Amazon, Createspace etc. From my own very limited understanding, Amazon etc do act as "tax withholding agents" on your behalf, but Apple do not. For the UK, this difference appears academic, as current "tax withholding" rates appear to be 0%. I will wait and see what the IRS make of this later...
When asking Apple if they even offered an official letter required for obtaining the personal ITIN (they apparently currently do not), I, very usefully, accidentally discovered that ISBNs are no longer required for "paid books" as well as for "free books." I pointed out that the current wording they use in the details they supply over this is a bit ambiguous, and they promised to review that.
To all others tackling this issue, good luck! ❤️