Given choice caching better than mirroring, but active things, eg search engines, can't be cached therefore have to be mirrored. Could get arrangement to have search software mirrored eg. These services are proven to be useful, and similar resources in the Web is what we need to support now. No, have home pages on separate file store. Best leave this issues to operational staff, a local issue.
Vendors generate lots of hype trying to sell powerful machines.
What you need depends on your usage. Universities may want figures to say what kind of machine you need, but can't predict this. What we can do is provide guidelines on how to setup machines so that it will be easier to migrate to more powerful machines. Potentially a useful appendix to Brian Kelly's document. If we have an infrastructure where caches and web masters are talking to each other then will get lots of support from within this.