You should look into FTP packages first.
Since this sound like it will be your only server, you should get a moderately beefy server with a good deal of redundant drives and storage.
Check out the free Filezilla FTP client & server. Surely a person would not use FTP to transfer 100 gigs of data? That would take a LOT of time and bandwidth. It would likely interfere with other clients. If a client has that much data to transfer, you may need a dedicated connection just for that client.
Did you end you choosing colocating? Or did you use a service provider? Just curious. 100gb is a lot of data to transfer via FTP.
We basically burn it on disks, and then ship those disks around.