As long as you can create an ftp session between the xserve box and the alfresco server then i would hope so.
Sounds like you will be wanting a large repo setup. As far as scaling is concerned, it's the usual things: put your DB on a separate machine with fast disks and on a high speed local connection to your Alfresco server, throw appropriate hardware at the Alfresco server itself - several multi-core processors and separate disks/arrays for the content store location (even go as far as multiple RAID arrays for the alf_data subdirs) and also the lucene index store location. A TomCat cluster could also help. If you make the right decisions early then it should be perfectly doable.
Thanks,
Kevin