XFCE @ Linux Guide:

• Developer: Free software community
• State: In active Development
• Languages: C

Xfce is a lightweight desktop environment aiming to be fast for weaker hardware while still remaining user friendly. The original author of Xfce was Olivier Fourdan and the first release of Xfce came out in 1997. Website

It has all the key features you need.

1. Window(s) Manager
2. Desktop Manager
3. Panel
4. Session Manager
5. Application Finder
6. File Manager (Thunar)
7. Settings Manager