1. Master server is essentially the same thing as a media server (plus it's a master). More simply put: the master does everything the Media Server does (and then some!), plus it coordinates the policy schedules and maintains the NBU database. It is, however, to your advantage in large-scale environments to use media servers.
2. Master and some type of device to back up to (and clients, of course!), like a tape library or disk pool.
3. Check with your local Symantec rep. on what's cheapest. According to our rep., Symantec is moving more towards capacity-based licensing, but 50 single standard clients is not very expensive. Your Symantec rep will best guide you.
4. It depends on what's important for you to back up and how. There are many different ways to do this. I backup each cluster node including all filesystems (I have a few exceptions requested by customers; e.g. Oracle database is not backed up, but the RMAN dumps are). You can create backup policies based on the VIP of the cluster if you only want to follow that filesystem for the backups. This makes it easier to find the files come restore time; otherwise, you have to remember which server the filesystem was on at that time, or run a simple query to find it. However, this backs up the files over the VIP, whereas if you have a media server, you could specify that media server instead and backup via SAN or direct-to-tape, provided you have the media server license, but you would also be limiting your cluster filesystems to the media servers (when you want good throughput). Again, you might want to talk to your Symantec rep. to see what's best for your environment and budget.
