If you are really thinking about building your product you should first do the alpha and beta. There is a strong community of tech people on Hacker News, ProductHunt and Reddit that will support your idea and even pay in advance if you can show a demo first. Give you an example: Dropbox. Drew (C...
I don't know about 100, but my very first three clients came through thought leadership articles. I believe that referrals and SEO kicked in after that for a good mix of sources.