Run Xenu over the site, export the results to a spreadsheet, sort the urls it finds so that you can exclude archive pages etc and there's your count. What difference does it make though? Seems to be a pointless thing.
Write as many as good posts possible but there is going to be a 20/80 rule as talked by Neil PateL on his blog - Quicksprout. Only 20% of your posts will out-perform so you may want to write as much good posts as possible and just know that only 20% of your posts will drive 80% of the traffic on your website. I hope this makes sense and answers to your question since there is no specific number - more is better.
Your question doesn't make any sense to me. I really don't know the reason behind why you looking for post count in a website? What is your purpose for it?