I don't have a definitive answer here for you on Plone, as I last tried to make it play in the Dreamhost environment a couple of years ago, and I could not get it to "play nice".
A lot has changed since then (not the least of which is my understanding of such things [wink)], and Dreamhost has upgraded the python package here at least a couple of times. it might be worth another attempt on my part, which your post encourages me to do.
It is my understanding that it is resource intensive, though to what degree that is true depends, I'm sure, on a lot of variables.
Not intending to "hijack the thread", but still relevant, I think, to your posted description of what you are looking for, you might give Drupal a hard look. It does work on Dreamhost, and some swear by it.
If I can find the time soon, I'll try to slap a test installation of Plone on one of my "dev" domains,see how it goes, and get back to you.