rubinetto - 6:15 pm on Jan 16, 2013 (gmt 0)
I'm also planning to move everything on one server
Not a good idea.
If all of your sites are quality and about different subjects then there should be no problem with having them on same Server. Lots of people do this.
However, if they are all about the same topic (as in your case) then I would not be surprised to see Google having a problem with it.
My impression is that Google tend to pick only one site from one Server for identical content.