I find it easy to use. I mostly use it when dealing with things like Word Perfect documents (which I occasionally encounter) or various other things that Word can't open.
While I've never done it in LibreOffice, it does appear that inserting charts in spreadsheets can be done:
https://help.libreoffice.org/Common/Inserting_ChartsAs to the other questions:
1. Pretty minimal
2. Yes
3. Open them in LibreOffice. No "conversion" necessary. And you can still save documents as .doc or .docx if you need to send to Word-only users.
4. See above
5. Yes - see #3. Can also save in other formats - Word will also open .odt for instance.
6. Not that I'm aware of - certainly not for free! Apple's Pages of course is another alternative to Word, but I've never found Numbers as good as Excel. Keynote is a nice alternative to Powerpoint - I've used that a bit.