Chapter count isn't an option as I mentioned to JimmXinu a while ago on another thread, as there is no definition inside an epub of what constitutes a chapter. You can't parse the content (chapters might be just numbers or images) and you can't use the TOC (it may or may not have chapters defined in it). To be honest I don't see any value in it as a statistic either - what does a "77" chapter James Patterson novel in comparison to a "10" chapter novel by someone else mean? To me personally it means absolutely nothing, because it comes down to the length of those chapters. Which in turn are more meaningfully represented by word counts and page counts...
As for your other request about not overwriting, something I have considered for a while is as per the screenshot below. This would allow you to run the various counts in isolation, rather than having an overwrite option. Unless anyone has any better suggestion this will be the UI for the next version...