Actually, I won't give players much creativity with technology at all. Things will be done very statistically tight and stream-lined, so players will not be able to invent techs that won't be in a pre-created, specific tree.
And, this galaxy is a grim outlook on humanity's capability to exist intergalactically. What I mean is that things will be dirty, grimy, and "old-school" style. No "human disintegrating" laser beams or particle rays, etc. Things will be clearly written out, to that effect.
And it will take time to get from system to system. Just like in Sekai, units/characters will have movement speeds, adjustable depending on what equipment you get for your ship.
I am going to leave it simple. By this I mean I might give players descriptive freedom, but these freedoms would not alter their hard, cold stats. Therefore, even if a player says his/her ship has weird, too-out-there technology, they still have to abide by the cold hard facts of their stats when it comes to combat and movement (though, nonetheless, I will give guidelines as to what exists in this universe).
And the game is not based on Firefly or Cowboy Bebop, I just gave those two as examples for you all to think about the kind of galaxy we would be living in. Grimy, dirty, and just coming out of a Dark Ages. You get the idea.
I will also probably have a Wordpress blog that will contain a "Galactic Bar" of sorts, which will feature missions found within various systems, to streamline the process of finishing turns. Just like in Sekai though, in between turns players can interact and story-post, and their stories may provide advantages for their character or faction.
And as for a character reaching higher to get to become the ruler of a whole star-system or even a small empire, and then later a larger empire: I like to think anything is possible given enough time and patience, but who knows if we'll even be around.
Anyway these are my ideas thus far.