Small map, heavily populated, and generate new random systems and toss them in to the existing network, possibly also adding new NPR.
Will also leave on Precursor, Swarm, and Invaders.
Now, on to the empire. Two questions: Should it start a certain way? Should the empire have a grand goal, or multiple goals?
I don't like conventional start, that's just boring to me. You're gonna get TN eventually, don't waste time piddling about with the simple start. But should a certain amount of tech be done, or starting conditions set? With Starmaster mode, I could make Earth have extremely bountiful resources, or set up Mars as a mineral hub, or any number of geographical settings. Then beyond that, the number of starting shipyards and other infrastructure can be handles, as well as starting tech. Playing aggressive, I'd suggest to go with engine, armor, and sensors more than anything else, as well as things like fuel efficiency and mining rate - if war games have taught me anything, it's that the winner is not the person with the biggest guns, it's the person who can produce the most guns the fastest. Large, fuel efficient engines strapped onto small, disposable war modules sounds about right.
And then, any over-aching goals? Shall we seek to produce a ship of a certain tonnage, or to colonize a certain type of planet, or to have a certain number of races in the empires? I personally want to go capping ships. Stealing special enemy ships like hive queens and invader anything sounds amazing. But there could be any number of other meta-goals available.