I can cover some of these:

5: Armoured Engines was a 50% increase to the Engine Space Units of a ship. You would multiply the MPs of a ship by 1.5 when determining the ORat for weapons, spinal mounts, carronades etc.

I would have answered the slow-firing question as well, but I needed time to think.

Heres my idea:

(S+1/T+1) x2

Where S is the number of shots, and T is the number of turns

Most weapons can fire at least once a turn, so thats okay. If we take a bog-standard ROF-1 weapon and chuck it into the formula:

(2/2) x2=2

The same as before. With it you can go up to any number of shots a turn.

But what if you want a weapon to simulate the heavy particle cannon? A beast of a weapon in B5W that fires very slowly, it would look ridiculous if it fired as often as a quad array. No problem with this formula. If you wanted a weapon to fire once every other turn, for example:

(1+1/2+1) x2
=(2/3) x2
or 4/3

That makes slow ROF weapons slightly more space-intensive.

But lets say that you have taken something really powerful, because you want to put multiple slow-firing weapons into the same mounting. I'm thinking of the unofficial Attarn Union here who likes their turret-mounted super-heavy Bil-Pro cannons. No problem. If you wanted two weapons that fired every three turns into a single mount:

(2+1/3+1) x2
=(3/4) x2
or 1.5

Simple.

Originaly I figured that a gun that fires every other turn or every other two turns would by the very nature of its slow firing rate be limited to a ROF of 1 by default.
   If I have a slow firing gun with a ROF of 2 I might as well drop Slow and make it ROF 1. It evens out at that point.
The main disadvantage to slow and very slow weapons is that they tend to get in a couple of shots in the game and then get blown away, so the SU mod tends to be a reasonable trade out.
   My main intention was that ship designers could build the uber weapons to represent a weapon system from a genre that they would like to play. These would represent the hard hitting but slow to reload/repower/cool down weapons in the genre. EX: Type R plasma torpedos, Photon Torps(Star Trek), Heavy Particle Cannons (B5), Wave Motion Guns, Death Star Main Laser, etc.
  I like the idea of expanded turn modes as it increases the value of maneuver in the game. Most of the people I play against design their ships with front forward primary weaponry since, turn modes aren't speed related, maneuvering is very easy and keeping enemies in arc equally so until very short ranges are reached.
  If increased turn mode was introduced how would this modify engines SU wise?. Could this be a tech level limit as well?
  On interceptable weapons fire, I don't think it would have to be done shot for shot, I would assume that only some of your weapons are interceptable and those would only be the attacks that would have to be defended against.
  Overall a "Defence Grid" type of equipment system would probably solve that but PDS already is that.
  I wanted to more accurately represent missile barrages or slow moving energy/solid attacks that could be "knocked out of the sky" with AA fire, along the lines of old style naval engagements.
  Opinions?
  Roy