Best server and/or cache setup for performance of multiple "related" blogs?

Greetings,

I have to install from scratch 6 or 7 blogs, all on the same Centos 6 VPS. As far as I understand, they cannot be handled with one multisite install, because:

• they are in different languages
• in different subdomains and/or subfolders, e.g a combination of blog1.example.com, example.com/blog2, blog3.anotherexample.com, something.example.com/blog4…

So I need to install one copy of wordpress and one database per domain. I have already done all the things below on single blogs, but in this multi-blog case I’d really welcome advice and best practices on how to optimize performance. My questions are:

1. is there a minimum amount of RAM/CPU type, whatever.. recommended for such a setup?
2. what is the best HTTPD server for such a load?Apache, nginx, others.., and with which setup/caching system/addons/proxies?
3. (related to the previous one) what caching plugin should I set up inside each copy of wordpress, and how to set it? In other words, what is the best place/way to do caching in such a situation?
4. anything else I forgot, performance-wise? MySql tweaks, etc..?

Thanks,
M.