Welcome to the forum, Rubini!
1. Never noticed that but then I never really had a close look at it
2. Well, the orbital period and distance to the sun is actually accurate in the game's data files, so movement should be too. They probably render it faster than real-time so the motion is actually visible to the player (similar to how games like Skyrim or GTA accelerate time, so an in-game day is significantly shorter than 24h).
For both of these issues, you could edit the
universe/systems/sol.system file after extracting it with
"datool" or "DatXtract". E.g. If you increase the "PeriodD" property of Earth, you should be able to make it move slower. Don't know about the rotation, though. There are three properties for that: RotationPeriod, RotationOffset and Obliquity - none of that really governs the direction of the rotation. Maybe by making RotationPeriod negative you can flip it, but that depends on how RotationPeriod gets processed internally by the game.
3. You can make ships move and rotate slower by changing the "Velocity" and "RotVelFact" (how fast it turns) in
universe\tactics\tacticstypes.ini for each shipclass or by changing "VelocityFactor", "SideVelFact" and "RotVelFact" of each engine (devicetypes beginning with "eng_"). This will affect their maximum speed as well, though - not just their acceleration or turning speed. This'll make the game considerably slower and might screw up certain missions to the point, where they can't be won anymore or where they might even crash the game.