Online. I got my parts from wherever they were cheapest (Amazon, Scan, etc.). Yes. Your graphics card is what you should be spending most of your money on. If you gave me a budget and a website for your area (like Greece (that uses the currency), I could probably even show you what I would recommend for your budget.
Done. You have NO idea how hard that was trying to buy stuff on a Greek website w/o speaking Greek D: Spoiler: The picture of the list
Nice comp what Mother board and video card do u have. I have to look through my stuff and check what specs I used to build mine ☺ I know I used Nvidia g-force GTX ...