Question #1:
I would like to upload the 482 pages PDF booklet for the series:
https://musicbrainz.org/series/4bc2a338-e1d8-4546-8a61-640da8aaf888
How can I upload a PDF to such a release group series?
Question #2:
Does it make sense to add the 1001 attribute numbers according to the chronological order in the booklet?
If yes, do we have any automatism to do that? Or can we get this numbers from Wikidata?
that may need to go in the bookbrainz website. i suggest emailing support@metabrainz.org about it
Is the 482 page booklet free to distribute? Are you sure there is no copyright issue with uploading something like that?
I very much doubt the publisher would want you distributing their book for free as they are still selling it.
As to adding the numbers to the series - you may run into a few issues there as there have been more than one edition of the book over the years. So there are now more than 1001 albums to be in the list as the list has changed over the years.
I think it works well enough without exact numbers as this is not really a series where they are ranking the 1001 albums. Just recommending you listen to them all at some stage in any specific order.
The more useful thing that could be done is to add more of the releases to that series. Clearly not 1001 in the series group yet.
With the same argumentation you could prevent to upload covers or even all the metadata, because for most of them “they are still selling it” is true.
This series is called
1001 Albums You Must Hear Before You Die (2005 edition)
so there is exactly one booklet matching it. The one from 2005 with ISBN 0-7893-1371-5 
The General Editor Robert Dimery wrote in his introduction:
“Of course, the overall choice of albums featured here is highly subjective. As editor, I take a lot of responsibility for compiling the list…
…One of the best things about putting together this survey was that it threw up a whole heap of suprises…”
I would say this is a clear statement for a compiled list [ordered by release date in the artists home country]. It is indeed not a “ranking” as in a chart/billboard list, it is just a subjective sort order. Isn’t that exactly what the attribute stands for?
I don’t want to go into this argument. There are better experts out there on what can and cannot be uploaded. I don’t need to pull your post apart line by line. I was only trying to give an opinion as to why 400+ pages of a book is a bit more than a CD cover.
Two things. Metadata usually can’t be copyrighted because metadata are facts about a product, not the product itself, and facts can’t be copyrighted. As for cover art, as I understand it, copyright was one of the major reasons why MB partnered with the Internet Archive instead of trying to go it alone with the CAA. The IA are masters of copyright law and know just how to present their collections on the web so they don’t run afoul of the law.
So instead of uploading the whole thing to the site, another option would be to add an annotation with a link to the IA: