mod proxy mapping file ? is this possible ?

I posted this in dev apache and the saw this specialized group for mod proxy

Thanks

I wish to do the following

1) there will be about 30 computers connected in LAN
2) I intend to use apache mod proxy in one gateway computer say gcomp1
and make all the 30 computers access the internet only THROUGH gcomp1

proxy is needed for ftp, sftp, ssh , smtp, pop , http and https protocols

socks ?

My questions are

1) Is this advisable? Is apache mod proxy better or worse than using
other proxies like socks.nec etc ?

2) Can apache mod proxy (with the addition of necessary modules)
handle all the above 7 protocols ?

3) *the most important* I want the apache mod proxy to be setup this way.

Say a client computer clientcomp1 wants to access an external ftp or
SFTP server ..extserver1

The user in the client computer enters the following details in
his/her sftp/ftp client

hostname: gcomp1 (the local gateway server IP address where apache mod
proxy is working)

username: user214214
pass: 23jjksdhafkhk

and once the sftp/ftp client connects to the apache mod proxy server
gateway gcomp1 the mod proxy apache server needs to forward/proxy this
connection to

extserver1
username: differentusername
password: different password

Maybe A mapping file should be able to configured in mod proxy to let
it know which external server to forward the request for a particular
internal username

like for example

user214214:
extserver1:differentusername:differentpassword

user453646:
extserver2:differentusername2:differentpassword2

and so on

The objective of the whole exercise is to secure all the usernames ,
passwords for the external servers and isolate them from the internal
users fully and completely.

Is the above possible in apache mod proxy ?

If not is there any proxy/gateway available which does the above ?

Thanks

chris