Philosophically, I'd rather separate a "media server interface" from the storage solution, because that allows more flexibility down the road and management flexibility with minimal impact if you have the physical, power, and cooling ability in the server room. Your web server could even be a virtual machine, or down the road (especially when talking about file servers) you may find you need to change your asset management or content management or some other aspect of storing and backing up your files.
I'd be wary of mixing your DAM software with the file storage because you may have more updates, maintenance, configuration, etc. work on that "application" which could affect availability of your file storage server. Generally for file storage you want a system that will keep your data available, and not have to fiddle with something that requires updates/configuration periodically outside the OS. It's too basic a function to have to take down because a web server is acting wonky or someone is attacking the web server the application has a bug in it that is causing issues.
Also, I'd warn against RAID 5. Look at my past responses regarding RAID or google for RAID 5 unrecoverable errors to know why, but basically, now that drives get really big, the odds of you having an unrecoverable error that goes undiscovered until another drive has a full-blown error are much higher, and you're asking for full data loss (hope you have good backups!) if you use RAID 5. Stick with mirroring or RAID 10, or someone else may offer other RAID ideas, but for high-capacity storage now I'd discourage RAID 5.
(and for cost, it's not too bad to assemble a commodity parts system and run something like FreeNAS with software RAID if it comes right down to it; everyone has their favorite turnkey open-source NAS distro to recommend. I personally prefer hardware just because it's easier when there's a failure to figure out which drive is bad; they're usually labeled off the card or there are blinkies, and of course most cards support hot swap. If you don't care, software RAID offers decent performance, but can be a PAIN for figuring out which drive is toast when the users are breathing down your neck to get the server back up...if the data is important, I personally don't buy into the argument that there's not budget. If your data is important you (the business) makes it a priority to get it working and reliable properly or they deal with the consequences of losing all the data or not having it available for hours while you try to get a solution patched in place and they'll suffer for making it a cheap slap-together form of management, and the IT person/team gets frustrated and moves on to a place where they're more likely to get treated properly instead of as an afterthought.)