I never heard of X3 before; is it any similar to Freelancer (it looks like it)?
I *think* I only played Freelancer briefly--and if so, it was the 2nd one, if there is a second one.
I recall that being more of an action-based, story-driven space combat sim...at least in the early stages of the game.
X3 certainly allows that, but it is much more. You can essentially play the entire game without combat, as a trader, if you wish.
Think of it as a complete sandbox space empire simulator. You can simply ignore the story line form the beginning if you wish and just do whatever you want. I do think you will need to do some combat and build a real fleet if you ever want to be involved in the story, however.
A lot of it depends on your chosen goal at the beginning. "Fighter" progression is the Terran race, I believe, and you can choose to to be a Trader which puts you as a different race. Depending on this choice, you essentially start on other ends of the galaxy. As a Terran, you start with a semi-capable fighter ship and can head straight to the story rather quickly, as your race is in the proper system.
As a Trader, you start about as far as you can get from the initial mission, with a slow and stripped freighter, and so you are essentially forced to develop your empire form the ground up to be able to even get a ship capable of reaching the first story mission and being able to survive.
I played briefly with the Terrans then switched to the trader race. Spent maybe 60 hours in X3 as a trader, never having reached the "start."
But I found that I preferred that, anyway. There are plenty of missions and goals to reach that exploration will reveal to you. You can even find specific derelict ships of various types that you can claim and upgrade, and add to your fleet. They are in very specific locations, so you can find them in the various online guides, which I found very helpful--as the economy is quite complex and some guidance early on is very helpful. There isn't much in game in terms of telling you how to play.