Its always great that a CEO of a major company like Ikea would take the time to reply to just one letter asking for advice, it really says alot about Ikea as a whole. Just imagine how many letters he must get per day!
I think you should indeed follow your dreams, no matter how many times your pushed back I think you should stick to those dreams, the business world is a dog eat dog world everyone is trying to make it somewhere, but the dreams and the will power is really what really counts. As for ideas for your next business, I think you should really start up something you have a love for (not just the skills), most entrepreneur's set up a business just for the money. When i'm working on new ideas I like to think of the stuff I love doing, and then brainstorm those ideas.
Good luck working on your new business!
Regards,
Adam
'A business has to be involving, it has to be fun, and it has to exercise your creative instincts.'
- Sir Richard Branson