As for the Data Science specialization from Johns Hopkins: the courses are not expected to be taken simultaneously, they are offered every month. I don't want to judge the quality but be prepared for a bumpy ride and various levels of difficulty starting from trivial (the 'toolbox' course can be done on a weekend) to unreasonable if you don't already have a solid background in the topic (the 'statistical inference' course got more dislikes than Giovanni's classic https://class.coursera.org/datasci-002/forum/thread?thread_id=36 and left many people frustrated) If you know a bit of R it's still a good place to pick up concepts and tricks though.