Given what you've said, I'm guessing:
- If you've been collecting them for some time they are probably valuable in some way.
- it's a low demand service: a few other people might access a video periodically
- Budget is tight
There's nothing wrong with what you've said, really, if you've got some simle requirement to make the data available for occasional transfer. The main thing is that a pile of USB disks in a drawer will last indefinitely. If you have them plugged in and switched on, the life expectancy is probably a year or three.
So, you might considered getting new disks at the highest density you can.
Or have it all working and configured, but only plug in the particular disks on demand (if that's not patently ridiculous)
Depending on application, you might even consider having everything plugged in, but only switch on a given disk on demand, with some relays etc. (if not even more ridiciulous!)
If the individual files are large (over 100 Gbyte, say) you'll get benefit from RAID simply for packing size. (That is, you won't have lots of disks with 90 Gbyte wasted space, because it's aggregated across the RAID set.) But in general I'm not a huge recommender of RAID unless you get a specific benefit you need: in your case, RAID0 gives you simplicity of setup but might be tricky when you outgrow it (no redundancy, just makes a big logical filesystem from smaller disks). Higher RAID levels will increase the required amount of raw disk space, and are probably not what you want.
Have you considered the file layout and whether the mounts are read only? I'm guessing you might get mileage out of a scheme like this:
If you organise the files in a sensible way, you'll give yourself a lot of space for when you need to move the physical parts around. I've organised some file servers of this scale like that and it works surprisingly well, once you get your helper scripts sorted out.
Then a big box of symlinks:
/disk/data/video1.mpg -> ../1/video1.mpg
/disk/data/video900.mpg -> ../15/video900.mpg
On the subject of access, are you sure you want FTP? Have you considered ssh (if you need authentication) or just old http (if you don't). I was so happy when I stopped having to lock up FTP servers. You say people will log in over ssh (so you'll have that already) ... what kind of work will they do? My line of thinking is this: 30TB of data online, how do we deal with accidental deletion, corruption etc.
Hope that's of some use. Tell us a bit more about your parameters and let us know your current thinking.