Answers in order:
1. You don't need any other software, the VPN is controlled through licencing. WinGate is licenced per machine, so in your scenario, you would need a 1 user licence for your work machine, and a 3 user licence for your home network. A 1 user licence allows local machine access only, so this would stop anyone else on your network at work connecting out through you, but if you want to get to machines at your home that are behind WinGate you will need a 3 user licence (the next one up after a 1 user licence).
2. As mentioned above, if you only have a 1 user licence on your work machine, then only this machine has access to the VPN. Also, your work collegues would have to set their Default Gateways to point through you.
3. No no other software is required on the client machine behind WinGate, as long as the Default Gateway of this machine is pointing back through WinGate. This can be set manually in the TCP /IP properties of the client machine or you can run a RIP client on it (QBIK has one available to download from
http://www.wingate.com/download.php.
4. Not anyone could connect in, because when you create your VPN on your home machine, a certificate is generated, with a finger print. You export this to the configuration file (from Gatekeeper), and then import at your work end. There is also a user name and password that the joining machine has to enter (much like you do to login to Gatekeeper). So someone on the internet would have to get a copy of individually generated certificate, as well as guess your user name and password to connect.
5. WinGate VPN can use any port you care to. By default this is 809. If you use this port number then you would need your work firewall to redirect UDP traffic on this port through to your work computer.
Regards
Neil