There are some things in the rules that arent too clear:
I'm not in the least bit surprised.
What is Construction time? Is it time in years? Does assigning more labor to a project decrease the time linearly? (ie: Project with 4 CT and 1 labor assigned takes 4 years, Project with 4 CT and 2 labor assigned takes 2 years, Project with 4 CT and 4 labor assigned takes 1 year, etc...)
Yes it's in years, as for labour, good question. On the one hand assigning labour should definitely increase the speed at which things are built, on the other hand there are limits on how many people can work on the same thing.
I think, linear reduction in time, but to a limit, large projects would have a higher limit, i'll probably have to come up with a limit for each construction.
What is the difference between using wood or stone in constructing something other than more Construction time and invulnerability to fire?
Well if you get besieged then ovbiously stone things would be harder to destroy, but mostly it's the fire thing. Fire isn't a huge issue for you guys right now, but as your city grows the threat of fire grows too, not entirely sure how i'll handle that, but there will definitely be a point where it'll be a real good idea to start replacing wood buildings with stone ones or risk losing the lot in a city-wide fire.
You'd also need to build certain structures out of stone; Forges for example are going to have to be stone.
Do tools made out of better resources give bonuses?
Correct, as do better tools.
Do we need tools to build constructions, or are they just an optional thing to get bonuses?
You do not, but they will reduce the construction time.
Do we need forges/tools/charcoal to smelt ore into metal? And to smith metal into tools/weapons?
Yes to needing tools and fuel, no to needing forges, although forges will improve the quality and reduce the amount of labour required.
Do we need tools/carpenter workshops to work wood?
No, but having such structures would provide bonuses to working with wood.
If we do have tools, are they all just generic ' Wooden Tools (basic)' or 'Metal tools (advanced)' or whatever, or do we have different kinds of tools, like carpenter's tools, smith's tools, etc...
Probably not going to get more specific than 'material tools quality', there
are limits