This is in a situation with OpenVZ, right? This is how OpenVZ works. I am not exactly sure how it is implemented in OpenVZ, but in networking terms the router knows which IP belongs to which mac address. Every packet from the router to the server is routed by mac address. As this is known by the switches and any bridging, it will direct the package to the right port and/or server.
If you want to have a second IP, simply use venet0:0. veth1 will point to a second nic, which you probably do not have.
Only when you use OpenVZ, the master can act as a host (aka node). However, in the situation of KVM and Xen, the master will just be the master and not run any virtual machine on it. But if you want to understand the difference between master and slave: the master is where the SolusVM control panel runs, the slave only listens to commands from the control panel.
This is possible and you can do this by simply adding extra IP's to the VPS.
There are many OSes. Actually, 5.3 is not supported anymore so you should not use that. Check out http://tdn.solusvm.com for more templates.