send the tracks u want to fade to a bus and fade them using the bus fader. you could also use automation on the bus channel. For individual tracks u could always use the fade tool or again automation.
Yup to re-emphasise what mtec says.
For individual tracks, turn on track automation and draw in or use touch/latch mode in realtime to create volume automation.
For multiple tracks either group the channels together and apply automation to on one... or output the channels to a Bus as mtec suggests :)