Building my first rig

Well after some cosideration and reading this forum I have decided to build my first rig. It will not be mine as my sons computer took a dive and now he is going thru WoW withdrawl LOL. So I have spec out the motherboard and cpu and ram but her is my first stupid question in the first build quest. Can I use the CDrom from his old computer also it has a flash card reader can I use it. I know these are not high dollar items but I hate to spend it here if I can put it towards, say a sound card. The old computer is 3 years old so is there a compatibiltiy issue with this older hardware.
2nd question is the Vid card I am considering for this system has a recomneded Min 400 watt for sli mode. How much more wattage is required to run the system and keep it stable. (now that i think about it thats a stupid question) depend on how many fans, sound card etc. Man I hate making decisions LOL. Back to the drawing boad. Thanks
2nd question is the Vid card I am considering for this system has a recomneded Min 400 watt for sli mode. How much more wattage is required to run the system and keep it stable. (now that i think about it thats a stupid question) depend on how many fans, sound card etc. Man I hate making decisions LOL. Back to the drawing boad. Thanks