We have full standard documentation here:
http://www.zimbra.com/community/documentation.html
The wiki is open for edit's so feel free to add new topics of expand on what's there.
- Splitting Zimbra would be hard.... Things are tightly coupled in many areas to give good overlap with the information
- we have lots of REST url's you can search the forums on ical or rest and get the format etc. You don't have to use SSL you can allow Zimbra to also expose http.
- SOAP is documented in ZimbraServer/docs/soap*.txt, there is also AjaxTk information starting to make it's way into the wiki.
- yes. even better use our iSync adaptor in the Network Edition to sync to your mac and then to your phone.