Can I just compliment you on the controls for the Fun Space Game? They sound great. I've had much fun with Colony Wars and their arcade-y approach, but it's refreshing to see something this realistic.
Well, space realism has always been ignored, but I think it would bring a breath of fresh air to make an internally-consistent (not strictly realistic, space is still a bore) space game.
So, just for a quick science lesson that so far only hard-sci-fi novels have adopted - movement in space is fast and constant. Your fuel does not determine your range, but your amount of "speed change." With just a gram of fuel, you can get on the other side of the galaxy, in time. There is no air resistance and a vessel with engines powered-down won't decelerate. You make a short burn, the vessel accelerates and then begins cruising indefinitely at the achieved speed, until you turn about and decel the same amount of time that you accelerated. Also, a vessel cruising, with constant speed, can turn at any angle, upside down, do a complete pitch-over, rotate in every way, and still move at the same speed in the same direction. So, you can be speeding towards one point and still have the entire ship pointing directly at the enemy, showing the smallest cross-section.
With your engines shut down, of course. In an atmosphere, merely moving an inch can make an aerodynamic object completely change trajectory, but in space only thrust will do that. This also allows space vessels to have no strict up and down, no wings or other aerodynamic accessories, so ship design that is bulky and unstreamlined starts to makes sense.
Also, large vessels actually have the potential to be thousands of time faster (but less maneuverable) than smaller ones - big fuel tanks equal long burn times equal higher cruising speed. A small stationary pirate vessel that detects a large freighter would probably run out of fuel before it could even match the freighter's speed, and the chase would probably go on for days.
So, small mobile fighter vessels (while they're impractical, it's a freakin' space game! It needs fighters!) would need to be deployed from carriers that have already reached a sort of "encounter speed" with the enemy. This could actually be used for creating something like rail-levels where the player and the NPCs are all independent, but the level itself is also "moving" to simulate everyone traveling at extraordinary (and realistic) space speeds, and the ships' RELATIVE speed is similar, so they seem to be traveling slowly in respect to one another.
Also, stealth in space. It's a complete myth abused in many sci-fi shows, but there is absolutely positively no way to achieve it. Everything that can house a human pilot will have a temperature of at least 290°K, which is 287° more than the space background, and thermal sensors can pick it up at millions of miles away. With the engines offline. If it fires up its rockets, even the smallest vessel is like a gigantic flaming beacon in comparison to the rest of the universe. Also, there's no horizon, no atmospheric interference, etc.
One solution would be to make the fighter vessels remote-piloted (the main character is actually on a carrier, which could explain how he survives his ship getting blown up), and the vessels itself are just cockpit-less computers with a chassis, but even then they have engines, power generators, bla bla... And "unmanned drone wars" doesn't make for good drama.
If you really dig the stealth-in-space aspect, I suggest you invent some sort of superscience fields or shields that somehow block any thermal signatures (and make them also act like radiators of waste heat, because gigantic radiator panels aren't stylish). It completely violates physical laws, but every game can afford some unexplained scientific miracle.
For some added realistic grittiness, ditch "plasma" weapons since they're ridiculous, make lasers sustained beams that deal little damage that increases if HELD on the enemy, and with unlimited range (they just dissipate a few million miles away), add kinetic energy weapons (electromagnetic guns would do fine for space combat), missiles, flares, make drive exhausts dangerous (as in, getting caught in a big ship's exhaust is unhealthy, and turning your butt towards an enemy is a sound tactic), etc.
When you determine what the setting's ships are capable of, it's easier to envision how the setting works, how space commerce and, by extension, space politics look like, how are space wars fought, how hard/easy space crime is and if it is commonplace, who guards commercial transfer orbits and how law is maintained in space.
I apologize for my geekyness, but I really like occasionally seeing an often hand-waved element in fiction done right. It makes me think: "Hmm, they really thought this through."