It is always a good idea to backup before flashing another OS and yes you will have to setup contact and other default setting after a successful installation. This will only be a one time process. Subsequent builds will come OTA and use the same settings.
/e/OS does not root your phone. You do not need to root your phone to install /e/. If you really want to root your phone then you will have to separately root your device after a successful /e/OS installation.
You can refer a document given here besides this there would be a lot of documents on XDA and other forums which you can refer.