It really depends on the number of users accessing those files.
You said its a FTP server. Is it a personal one or public one ? Who will be accessing those files ?
If its just you then you wont need high amount of ram and 100 Mbps connection should be enough.
But if say thousand users are going to access it and the number might increase in future, a 1 Gbit connection would be a good choice.
Proc and RAM may not be as important in this case, however disk performance and disk controller performance will be crucial.
SoftLayer has very comprehensive storage focused solutions, and has one DC in Amsterdam which will suit your needs. Not to mention awesome network performance, supreme support, and a very automated system to handle your server and infrastructure.
PM me and I can help you get in touch directly with a Sales Engineer
It seems to me that you just need a server with lots of hard drive space and nothing much else. Typically VPS's are sold in increments or fractions of a server, inorder to get lots of hard disk space you also need to get lots of RAM and cores of CPU. (which you really don't need) I personally would just host a simple server (with the exact specifications needed) myself at home (or in a data center)