The nymphs are possibly inspired from Dante manuscripts

[Jorge_Stolfi]

1. Every part of the MS is an original composition (until we find evidence of the contrary)
   
2. The artist was still a child of their time, and I assume they had access to some books.
   
3. The artist was not extremely skilled. 
   

Agree completely for 2 and 3. I would even say "child of their time and place".

As for 1, there is no evidence for it.  On the other hand, there is evidence to the contrary; it is just not generally accepted yet.  So I would say that the prudent choice is to leave that point open.

Put bluntly, I think they borrowed forms, poses, sequences.. from the world around them, in part because borrowing makes drawing much easier, but also because everybody does it. But they built something new with these inspirations.

That "they" conflates two (or more) totally different persons.  One of them invented an original alphabet (and cipher, if believe that) and had a lot of things to say about various "scientific" subjects, including herbalism and astronomy/astrology.  The other could not divide a circle into four equal parts or score baselines and margins to guide his scribing.

So it is hard to tell which parts of each figure were defined by the first guy, and which parts were improvised by the second one.  Even when we can tentatively identify a figure as being inspired on the Balneis, Taccola, Oresme, a certain German almanac, etc.

What would the implication be for timing and location of the artist, and/or the contents of a library they were able to access?

Maybe f85r2, the "four ages of man" is the most likely to provide that information?  I understand that Taccola, Oresme, and the Balneis were widely dispersed in Europe. But f85r2 was conjectured to be as a "cousin" of the illustrations of "four seasons" in a certain German almanac.  Would that book have been known outside Germany/Austria/Switzerland?

All the best, --stolfi