I have a few questions I hope you shall be able to help me with;
Happy to help! Though I'm afraid I don't know the full answer to some of these.
I understand an active sensor can never spot beyond its maximum stated range, regardless of the size of the object to be spotted. Does that hold true for passive sensors? If an EM sensor can spot a 1000 strength emission at xkm, could it see a larger emission from beyond xkm?
Passive sensors don't have a maximum range, no. This is particularly obvious for highly populated planets, which can have EM and thermal signatures in the low millions; at that point even the most primitive sensors can see them from extremely far away.
How do I repair the armour of a PDC?
As far as I'm aware you can't. You can't upgrade them either.
If I make a PDC with hanger space, should I include fuel and MSP supplies?
Fuel isn't necessary unless you want to roleplay it; you could just launch and have the parasites refuel from the planet. And in fact at one point having PDCs with fuel tanks was a good way to get spammed with out of fuel messages, but this may have been fixed. MSP could be useful for performing repairs on docked craft, but wouldn't be strictly necessary either.
I occasionally find a system with multuple stars, where one star is a long long way away. So far away I can't send a geosurvey ship there without tanker support. I've noticed I can add geosensors to a missile design. Can I use a design with a 'Geo Sensor Strength' of less than 1.0? Will I need an active sensor and fire control that can see billions of km to target the distant planets?
I believe you can launch missiles at a waypoint in orbit of a planet without needing a sensor or fire control for it, but I've never tried it so I can't give specifics. I usually ignore long distance binary stars.
Can someone tell me how to design a functioning mine (the explosive in wait, not the hole in the ground)?
Again, I have no personal experience, but I think if you design a missile with a sensor but no engine and include standard missiles as a second stage, it will launch those missiles when it detects a hostile vessel within the distance it's set to detach a second stage.
What does the recreational module do for a ship?
A recreation module provides a location for shore leave (but only when in orbit of a planet, I think).
What do the 'expand civilian economy' techs do exactly?
They increase your wealth generation. I think they directly increase taxes and also increase the supply and demand of trade goods that your civilian lines ship around to generate money.
Is the cost of installation construction based on the total number of construction factories or the total BP generate from those factories? Am I driving myself into the poor house researching the BP tech line too soon?
The wealth cost is based on the number of BP/CP/RP produced, not the number of factories. So techs that increase the production of factories/shipyards/research facilities also increase the wealth cost of operating them at full capacity. Note that you'll never lose out by increasing the tech, though, since producing the same amount of things will cost the same amount, it will just get done quicker.
Is there a cost of maintaining a fleet beyond the minerals they consume through maintenance facilities?
There's a wealth cost too, I think. I would assume it's 1 wealth per unit of minerals consumed in maintenance, since that would sync with the rest of the game's mechanics.
If I have multiple ships carrying maintenance modules, is the maximum ship size supported the sum of all maintenance ships? Or equal the maximum size supported by one maintenance ship?
It's the total. You can use multiple maintenance ships together to service larger ships.
If I use a scouting vessel to probe ahead of a battlefleet with either a thermal sensor or an EM sensor which would be wiser to use?
I'd normally use thermal, since it's harder to hide from; thermal emissions come from a ship's engines, whereas EM comes from active sensors and shields, both of which are much easier to turn off. On the other hand, an EM sensor not only tells you where the enemy is, but if the enemy is looking for or targeting you. The best solution, if you can manage it, is to use both.
I often see people appraising others ship designs and saying things like 'too slow for a plasma generation ship'. Is there some rule of thumb for a speed to aim for, or its it purely a personal opinion?
It's to some degree a personal opinion. I usually aim for a quarter to a third of a hull to be engines, for instance, but there's not really a right or wrong answer. However a lot of it is experience with what's most effective.
How/Where do I assign a task force commander & his subordinates?
I usually use the f4 personnel menu, and select the "Staff officers" assignment type filter. Knowing Aurora there's probably multiple ways to do it, though.
Thank you.
You're welcome.