Run ISPConfig 3.01 on VPS

[newbie2008]

Thanks to ISPConfig working team for such amazing package, I have two questions regarding to ISPConfig version 3.x;

1) I plan to install in the VPS environment such as OpenVZ or Xen, what is the system requirement, for example 256MB RAM is the minimum or please can you specify other requirement should meet with.

2) I knew that the ISPConfig version 3 can support multiple server, in case A, if I put everything (DNS, POSTFIX, Apache, FTP, MYSQL etc) on one dedicated server while in case B, I separate MYSQL on one VPS and POSTFIX on one VPS, the remaining services on one VPS. There are total 3 VPS servers in case B. Should this partitioning provide better stability in case B instead of case A? Assuming the MIPS of one dedicated server is similar to three VPS I used in this case.