Hi
Broadband over telephone wire ADSL. Upload speed is slower than download speed
Once you get through modem router to Ethernet the speed is the same in both directions
If both devices are capable of 100 MB/s the connection will be at 100 both ways
10/100 speeds means it can support other devices with any of these speeds
The latest raspberry Pi is more powerful than the earlier versions
If you use the media centre operating system designed for the Pi you should be ok
(Extra cores , speed of CPU ,extra ram)
Regards
Mike Barnes