With a laid back style but hardly cautious, Opendoor Co-founder and CEO Eric Wu had a pretty good 2016, starting with news that his Phoenix-based real estate tech startup received $80 million in its third round of funding and ending with $120 million in funding and a $1 billion valuation. His hot firm was buying and selling homes at an astounding velocity — at times putting 20 homes under contract in one day — over the summer in Dallas, Las Vegas and Phoenix. Wu’s business is making big and small changes to the home transaction process as much of the industry watches with interest.