First things first,what is your budget? Will your build need to include an operating system? Will you need a monitor?
In my opinion it is wiser to have 2 separate 500GB hard-drives as opposed to 1 x 1 TB drive in case your main drive fails which could result in the loss of all your files, whereas with the 2 drives 1 can backmup the other. A soundcard is not really necessary as motherboard onboard sound is pretty good these days.The Killer 2100 card is also not really necessary, have look at this respected review site. Killer 2100 If you post answers to the above questions you will be able to get the advice you are looking for.