Thankfully you can start single player games just by yourself. I think I forgot to turn off neutral players so the other planets are defended, but it's a good way to get a feel for the game. Unfortunately when it's just you there no other target for pirate attacks...
I'm enjoying it so far, even if I really don't have much of an idea about what I'm doing. The empire tree really does make controlling things a lot easier, and watching my units do things the smart way (no micro!) is a freakin' dream come true.