You get full root access (for Linux) or full administrator access (for Windows) to your server. Therefore of course you can install any software you want on your server.
The traffic is unrestricted, so you don't have to care or worry about how much traffic you use every month. Besides, the bandwidth is pooled, which means that the whole data center distributes a bigger bandwidth. We don't bill our clients with exceeding traffic limit.
Sure thing! We provide the cPanel/WHM and Plesk with various versions available.