1. What's the aim of a game with almost infinite playground(final goal)?
2.How will you make exploring the universe fun? Will you have main zones with many events where players can meet? For I resisted the idea of getting more than a galaxy or even too many star systems in the galaxy. Players wont meet up if they are too far apart!
What's "fun" in your opinion? In mine, its discovering new worlds, obtaining information about them, planning colonisation and terraforming.
3.How did you make the galaxy's dust clouds? With billboards?
Yes, galaxy models are made from billboards (light - yellow and blue and dark - dust).
4. Are you planing on adding collision to the planets? Won't it rise the minimum CPU/GPU requirements?
Did you read the TODO lits?
5. What do you think of Infinity? It has a lot more attention than the SE !
I think it will be a good new space opera.