Dead easy. It's designed to do exactly that. See http://docs.django-cms.org/en/develop/how_to/install.html, which covers most of the bases in some detail.

Very easy - django CMS is Django all the way down. All addons are simply Django apps, the templates are Django templates, etc... So if you know Django you'll find it easy to develop for django CMS. It's quite common to find sites that started as bare Django sites and evolved by adding the CMS to it.