Thanks everyone for answers.
As it seems that those PDFs (or rather their reasonable support) is the biggest problem, I think that I am willing to relax that requirement and read them on my notebook instead.
I like the idea of ereader mainly because of the form factor and long battery life. If I have bought a tablet I would have neither...
After processing your thoughts I suggest these altered requirements:
Should have:
- 6" e-ink screen (those 9"+ are imho overpriced),
- good quality display,
- support for czech letters,
- no vendor lock-in
USB support has moved into the bonus section. The rest stays the same...
Thanks again, waiting for your input.