Sounds like you've got a very interesting and ambitious project ahead of
you.  The setup I use for my home VAXen meets at least some of your
criteria. 

Basically I've got an Intel server which acts as a boot and fileserver for
the small collection of VAXstation 3100s I shepherd.  The VAXstations are
diskless except for one which I use for playing with the NetBSD/VAX SCSI
code, but they all boot from the network.  The bootserver information is
set up such that all of the VAXstations share a comon /usr filesystem
which helps a great deal to economize on space.  It also makes
upgrading NetBSD versions across all the machines relatively simple.  Then
I take the remaining non /usr directories and set aside unique copies for
each individual VAXstation, each of these requires only about 16Megs of
disk space. 

I like using an Intel based server because of it's speed, and they are
really fairly inexpensive to feed and grow.  They are also very well
supported by all of the free Unix OSes.  Storage solutions for Intel boxes
are very good as well.  With respectably fast multi-gigabyte IDE and SCSI
drives being so inexpensive these days, an Intel box can make a fairly
decent file server -- well, within the constraints of a tight budget at
least. 

I know this is a personal preference thing and it does depend on just
exactly what you're trying to achieve, but if I were to wind up with say
an assortment of VAXstations and Q-bus MicroVAX machines I think I'd set
up the VAXstations as diskless clients of a zippy fileserver.  Given
enough clients you could even stick multiple ethernet cards in your server
to split up the client net traffic onto different ethernet segments (I'm
assuming that no one's going to be donating any switched hubs to you any
time soon :-)  Then I'd use the Q-bus MicroVAX systems and any local disk
storage they had to act as special function servers: e-mail, WWW, FTP,
DNS, maybe even serving less often accessed or less speed critial NFS
filesystems -- perhaps use some space on one to hold all your man pages? 

-brian.
---
Brian "JARAI" Chase | http://world.std.com/~bdc/ | VAXZilla LIVES!!!