It sounds like the way DreamCompute works is a bit different than what you're used to. Every customer gets a private network with a router. All new instances get a private IPv4 address and a publicly addressable IPv6 address. If you'd like one of those instances to have a public IPv4 address, you assign it a "floating IP" (that's an OpenStack term).
You also have the ability to create security groups, which are essentially instance-level firewall rules. The default rules allow all traffic between machines on the private network and external traffic for SSH, HTTP/S, and ping.
If you wanted a second IPv4 address, it would need to be assigned to a second virtual machine. All traffic would be routed through your router to that particular instance.
As for having two separate networks, right now we aren't providing that option. Each customer gets one private network and one router. We understand that doesn't work for everyone, so we're working on removing that limitation and should have more news on that later this year.