Hi,
1. Content can be created on private pages protected by roles and then published by changing the allowed view roles to all users. There is also a content workflow with role based approval but mainly for the Html content feature, it is not yet implemented in other features.
2. No pages do not, but content features on a page can be scheduled for publishing and expiration. Really having content expire is not the greatest idea in terms of SEO. Once the content is indexed by search engines you don't typically want to remove it and have broken links or pages not found. Cool urls don't change and don't go away.
3. You can host multiple sites using 1 installation and 1 database. It is possible to share users and roles across sites in an installation but it is not currently possible to share content across sites other than by exposing and consuming RSS feeds (and then only the features that support RSS). There is no storage of translations for specific content items. A forum instance in one site is not related at all to a forum instance in another site. If a user posts in the forum it will appear only in that forum and it will be in the language that the user posted it in.
4. Very easy, try demo.mojoportal.com, go to Admnistration > Site Settings, you can browse and choose a skin which changes the entire appearance.
5. Probably not easy, mojoportal is meant to be the framework for an entire site, there is no magic glue for integrating things it requires knowledge of both things you are trying to integrate to come up with an integration strategy or determine how much effort is involved.
Hope it helps,
Joe