In personal scale, if a target is furthur away than a weapon's range, you add a difficulty die for each range band (on top of the difficulty die for the new range). So an expert pistol marksman shooting at long range would have a difficulty of 3 purples (for range) plus 2 purples. (2 range bands out of range)

Can a starfighter with a range of short on it's torpedos, fire them at a larger ship from Medium range? That is, a sillouette difference that makes a normal combat check a Simple roll, with only 1 starship range band of out-of-range penalies... is it possible, and if so is it 1 purple, 5 purples (one per personal scale range band per planetary scale), or what?

You need the Sniper Shot talent to shoot beyond the listed range. This applies to both personal and starship/vehicle weapons. Sam has said that he doesn't normally allow Sniper Shot with starship/vehicle weapons, but he makes an exception for the Advanced Targeting Computer attachment.

Yeah, you can't shoot past the listed range in personal scale either without Sniper Shot or a mod.

As HappyDaze has indicated, and I'd use his advice. That having been said, the reasons for a given shot having a specific range can happen for any number of reasons. In some cases, such as a slug thrower, beyond a given range the weapon is simply not reliably accurate because of gravity and other physics, and therefore needs a trained sniper (sniper shot talent) to coax the maximum performance out of a weapon. In the case of blaster weapons, the energy in a given blaster bolt may simply dissipate too much to be effective beyond a certain range.

In the case of Proton Torpedoes, they're distinct from missiles as they're described as an "energized missile" which I take to mean as hovering somewhere between a blaster bolt and a missile. You may fire a Proton Torpedo at longer range at a bigger ship, but the energy that makes the weapon as dangerous as it is may dissipate before it reaches its target. So this may also play into the issue of range with a given weapon. So mods or talents allow for the weaponry to operate beyond their normal ability, but without them they are left to their usual limits.