few pointers:
• don't think how many blogs, think how many keywords
• pick 2-3 top priority related keywords and produce kickass content on it for atleast 3 months before you go beyond
• how many to publish? let me answer it this way: how quickly can you produce blogs which are high quality, unique and useful? now answer how many of these can you distribute and do a good enough job?
• the limiting function is not number of blogs but number of quality blogs and your distribution muscle.
• no advice is good advice here, just get started, measure everything like a maniac, optimize, iterate.