Here comes the PDF part.
First: It's working. Second: With some flaws.
So I had some PDF-books and have to say, they are readable. You can change the size in percentage, but only in 10 percent steps. Reflow works too, but isn't helpful if the book is already in the 6 inch range - except you want extra big letters. There is no reflow over multiple pages.
What is thought well but done stupid is the crop function. You have the margins removed, but the last line of text is covered by the status bar. So it may be usable if you have the page number at the bottom of the PDF but not otherwise.
A firmware update should cover this.
What I wish to have, because I learned to love it on my 505 with PRS+ is the extension of the status bar with battery state and time. These two info I really miss. At the moment I have to read a lot more to drain the battery and see, when the "low" warning appears and how many pages then are left to read.
Now to the glowing vs. ambient light. The preference is really personal.
I personally don't like to read in the dark with only the reader glowing, which would be the intended case for the light. As support for low ambient light it works really well. So reading in candle light is okay. Or when the sun is hidden behind clouds these days. I just need some light around.
Also I noted that the lighting isn't continuous over the screen. You can see slightly darker areas. Not as a pattern, but visible. However this does not hinder the reading experience.
The dictionary I haven't uses yet, I will try it today evening or tomorrow. If it works - fine. If not, I have my smartphone with an online dictionary app in reach. ... Thinking of it, I like the dictionary on a separate display - to have the context in view. But I will try it out for you