CentOS - Nov 2006 - request for optimum setup configuration

hi,

I am required to take text/doc files uploaded to a share/directory in a 
static ip, do some processing on this queue, convert the file format and 
save the results in a directory for it to be downloaded (or I could 
upload the same to another share/folder in another static ip).

volume of files is about 1-5 files/second of about 50KB to 100KB each 
and the converting and delivery has to be in near real time. The actual 
conversion is on external systems on a seperate subnet and this planned 
server is for just handling the input and output automatically.

I do not know yet if i can use a vpn as the server that provides the 
data allows this or not.

I had planned to put up a centos 4.4 based secure ftp server with two 
diretories one for incomming files and other for completed, both 
password protected. the access to the directory will be limited to the 
ip addresses that are using this facility with iptables.

Static IP
      |
Firewall------(public ftp)
      |
(private network 192.168.xx)doing the actual sork
      |


could someone with more experience than me (read newbie) comment or 
suggest a better approach than the one above or point out security 
issues as the data must be secured at all costs.

Thanks for your time.
-- 
rm