MU Network Server Related question – 500 error , memory, etc

Hi all, we rolled out our mu for students yesterday and almost immeadiatly it starte crashing. at first it was memory, i increased wordpress memory to 128m and it fixed that problem, but then we strated getting 500 errors in the admin (cacheing on the front end)

I’m using prosite, easyblog, and well allot of other plugins.

were hosted on a dreamhost vps.

Any suggestions to what I can do to the install and to the server to get this site running better????

Would disabling some plugins help?

What about themes??

One of the options in the server is disable mod_php, would that be a bad idea?

What about php x_cache?

What should I have on the server end to help? were trying to avoid a more expensive server for budget reasons, but we might have to upgrade.