Forged Alliance CD is all you need to start playing (FAF supports 3596 3599 3603 and steam versions of game)
(CD key only will be needed to install game)
FAF uses indestructive patching so just don't worry and let it do it thing, FAF will not even alter your FA instalation
FAF is much more advance than GPG and steam version (steam version is newer than GPG, but it uses 3603 patch and FAF is already like on 3640 or so xD)
FAF has nice features of map/mod/patch autodownload
If you try to join to game where you have no map/mod it will be downloaded automaticly
if you try to watch old replay of different patch, game will be patched to different version automaticly in a matter of 20 seconds
you can spectate games live with 5 minutes delay via "live replay" feature that is now enabled for every player
there is 2 rating systems, one for custom games and one for ladder games
There is reworked campaing with increased difficulty and what is more importans COOP up to 4 players and ability to enable mods
Improved explosions, inproved performance, improved AI and improved UI...
Tournaments are still happening
Games still being casted on youtube
Twitch streams also happen time to time
you can also join FAF chat via any kind of IRC client.. like lets say on your smartphone
FA is alive!
Thought have to notice that game balance and gameplay changed over time with patches (changed in a better way)
but if you neber played before, it probably does not matter for you
Welcome to FAF!