Lots of issues raised there.
Normally the first port of call is to ensure that alfresco is always available. So look at clustering and fail over to a hot or warm standby. You will find various threads on these forums discussing how people do it from the simple to the wierd and wonderful. There are many options (Alfresco is very customisable) and that's probably where your sys admins should be concentrating.
Yes there's a potential issue with needing to pull content from file server to serve it up via another protocol like NFS however the content store lends itself to caching very well. There's also a caching content store in Alfresco Enterprise for use where the file server is expensive or slow. There are also many third party filesystem tools which can cache, cluster and manage different volumes.
A production run with "hundreds of thousands of documents" which are accessed via NFS sounds like a slightly unusual requirement for alfresco. Perhaps if you posted rough details of what you are trying to do there may be other options? And you can read the content store "by the back door" if you don't care about things like security which a big batch job typically may not. (Just don't update or delete content!)