Developing a Scalable Website using Php

[Eric E.]

I am going to develop a social + professional networking website using Php (Zend or Yii framework). We are targeting over 5000 requests per minute. I have experience in developing advanced websites, using MVC frameworks.But, this is the first time, I am going to develop something keeping scalability in mind. So, I will really appreciate, if someone can tell me about the technologies, I should be looking for.I have read about memcache and APC. Which one should I look for? Also, should I use a single Mysql server or a master/slave combination (if its later, then why and how?)Thanks !