FTP for LAN and nothing else

[Filezilla-4-Eva]

Hi, this is probably a total noob question but,
I run 2 computers behind a router, therefore both use the same IP on the internet. Instead of opening my NETBIOS for file and printer sharing I'd prefer just to FTP the stuff between them.

The version I have installed at the minute by the way says in the "About Box" : "Filezilla Server Verion 8.8 Final".

Under 'settings->passive mode settings' I have it set to default. Basically i want to FTP between the 2 computers, but don't want anyone else outside the LAN (on the internet) to be able to access either one's FTP. Incase they scanned for them (even though I have a firewall). As far as I understand, if I leave this setting as "Default" this should be the case?
To make the FTP accessable to the internet I'd have to enter my IP in here? So I should be safe enough as it is?

I want only 1 IP to be able to log into an account an at a time, and for that IP/User to be open to download multiple things at a time. This means I should set 'Users->General->Max Connection Count : 1' and 'Users->General->Connection Limit Per IP : 20', yes?

Is it possible to only allow a specific IP address access to an account?

I use Getright to download from the FTP Server, I can log in ok, but when I try and download anything, in the FTP Server window on the other computer it shows as "Not logged In", whereas it seems "Logged In" while I browse? It's as if it treats the browser window as 1 user and the download window as another/non-logged-in user? So after I find the file and start the download, I must logout the browser so the download can start. Any suggestions?

Thanks for your time,
And great prog.