Journal: one server, or one server with many virtuals?

So, I am in the planing of expanding my home network. I am going to include, a wordpress blog, email (including webmail, imap, etc) webserver (separate from wordpress), proxy server (with content filtering), file server, mysql, and a jabber server. I plan on centralizing logins by openldap. I will other people outside of my home accessing some of these services. My question to the masses is: should I run all of these on one box, or on a slightly bigger box in VM's. I am looking to keep cost down, and also to keep the box as power efficient as possible.