As far as the 1000S goes:
- SDHC cards work fine, at least confirmed up to 16GB, but you have to (re)format them on a Mac/PC if that becomes necessary (not in the reader itself).
- CHM files can be read using the free
FBreader application, and optional support to open them with it automagically
exists as well. How large, I don't know; haven't used one yet that didn't work.