Cache Private Project

1. i need an optimization on my server (memcache, opcode or anything that you want). I trust you so you can choose the cache methods. 2. on my server i try to install opencart via plesk but i get an error. the error is : Error: The following problems with requirements were found: The 'mcrypt' extension was not found. 3. on old server, any other subdomain gets an error 500. Sometimes is error 400. but becareful there because now the site is online