... how would you present all the different planets, space stations and stars? In Pirates, all possible destinations are single points on one large map - there are no cities within cities. But what about a space travelling vessel? One star system could consist of several planets or other points of interest.

I am torn between simply using planets and stations on the galaxy map represeting their systems to streamline sending a spaceship from point A to B, or stick to proper starsystems which could then consist of more than one possible trading port which would allow for inner-system trading but could be cumbersome to handle for the player.

Which would you prefer? Or can you think of another option?

How would intrasystem trading make the gameplay more interesting/fun?

I think it comes down to whether or not players can accept a more abstract map that consists of planets only rather than proper solar systems. Intrasystem trading could have some advantages, like relative safety from pirate ambushes, while on the other hand not being as profitable as the more risky intersystem trading.

Would you need to represent all the planets at all levels? The trade needs of a star (supply and demand) would be the sum of the needs of all the planets in the system. As long as you are travelling between stars you don't care about individual planet needs as much (yes you might miss out on some deals). Once you enter the system it could then be broken apart into the different planets and then on down to the different cities. You could even show supply/demand for each items as an average of the system then show the planet/city with the highest/lowest supply/demand along side.

Interesting suggestions there, Drethon. The average of the system would probably become more and more interesting once your fleet gets too large to micromanage every last ship and planet or things get automated, so you won't have to search every last planet unless you want to invest the time to gain higher profits.

On a more general topic - realtime or turn-based?

I think realtime makes sense in a game like Pirates were you are navigating only one ship at the same time, yet all games I have played in which you are in control of a whole fleet of transporters (1869, Ocean Trader etc.) were turn-based. In a TB environment certain things would be easier to handle, like docking fees (each turn would cost a certain amount of money) or trading/taxi missions (it's easier to tell whether or not a ship will make it from System A to System B in a certain amount of turns). On the other hand, realtime would make it much easier to introduce a multiplayer option since you wouldn't have to wait for other players to end their turn, though you could get around that by a time limit per turn like some boardgames do, either from the start of the turn or as soon as the first player ended his.

Any thoughts?

The other option to consider is real time, but with a pause button. This is the approach that Patrician 4 takes. This allow players to manage many fleets at once if required, but would present a problem for multiplayer.