Stockholm is not home to IKEA and has never been. The company originated in Småland in southern Sweden but is currently headquartered in the Netherlands.
By the way, unless you’re traveling on the weekend when there are deals available I would definitely avoid the Arlanda Express train as it is phenomenally expensive – even for Sweden. If two people are traveling together you can get a taxi to anywhere in central Stockholm for less.
It may be cheaper to get budget flights to Nyköping or Västerås with a coach connection to central Stockholm. It’s a fantastic city, especially the area around Gamla Stan.
Stockholm is not situated on 14 islands in the BALTIC SEA. Although some of the newer outer suburbs and satellites do sit on islands where the lake Mälaren meets the sea, the Gamlastan (old town) and all the major central islands sit squarely in the lake itself.