1. If I have a functional well, and channel above it and place another well, will it be useable?
Unfortunately no.
2. One of the things I put in my forts is a mist waterfall in the dining room. In my latest attempt to do it without pumps (brook water from above, that gets directly drained into a chasm), the tiles surrounding the place where the waterfall holes are (covered by grates for safety) seem to be randomly splashed with 1 depth water. What is causing this? The water above it is de-pressurised twice by diagonal flows, and the water falls down a 2x1 hole with grates ("##"), into the dining room with the same holes beneath it, and down the next Z-level to be drained into the chasm.
Here is how it looks in my dining room:
11111 1= Water that's splashing around and drenching the tables near it >.<
1#1#1 #= Floor grate through which water is falling
1#1#1
11111
And above it:
WOW WOW
WOW WOW W= Wall
WOW#W#WOW O= Floor
WWO#W#OW #=Floor Grate
WWWWWW
Why is the water splashing around the holes? Is it from my dwarves running through it, pressure issues, draining issues, or something else? Will 1-depth water that is drenching my tables affect the dwarves eating on them? And is this potential to cause a flood later?
It's possible the water's behavior is just causing this. Unless it starts to actively overflow, I wouldn't worry about it. You do have it linked to a lever above the river, right?
3. I have a GCS that I captured (with casualties) in a cage trap, and tamed it. Due it to killing a few dwarves, my attempts at using it for endless GCS silk have been... unfortunate (it is currently in the cage it was caught in, as a zoo atraction and dwarf party spot). How can I use a tamed, dwarf-bloodthirsty GCS for fun (goblin abuse) and/or profit, A.K.A. silk generation (preferably without dwarven casualties)?
There are two designs I can think of.
The first is a GCS arena. Create a room and pit/release the GCS in it, with the only exit either a forbidden door or, better yet, a barrier linked to a lever (drawbridge, floodgate, lever linked door, etc). Pit, drop, or order creatures - friendly or hostile, doesn't matter - into the room. The GCS will spray silk and you can collect it. Now you need a GCS recovery mechanism. Create a tunnel with a chained puppy or stationed soldier at the end and a cage trap in between them. When you want to recollect the GCS, open the tunnel. The GCS will eventually wander into it, caging itself, and then you can gather the GCS silk cloth.
The second is Silker. The basic design is like so
wDwB w = wall
wGf B C f = fortification
wDwB b = drawbridge to control line of sight
G = GCS
C = target animal (usually a kitten).
The doors need to be set so dwarves can path through them but cats cannot (be sure to make sure the dwarves have no reason to path through it, otherwise the GCS will eat him and escape). A GCS will only spray silk if they can path to the creature. Pet impassible doors count as a path, even though the GCS can't get through. When you want to create silk, lower the drawbridge so the GCS can see the cat. It will try to attack the cat, realize it can't reach it, and spray it with silk. Then pull the lever again to raise the drawbridge. Now the dwarves can gather the silk without freaking out because they can see a GCS.
4. I have tame wolves, tame giant bats, and tame war dogs. How good are they in combat by comparison to each other?
My guess? Giant Bat>War Dog> wolf. Dogs get a pretty serious power boost from training, while a wolf can kill a dog the inverse is true for a war dog. Giant Bats are downright scary.
5. How do I make my tame elephants attack gobbos, and can I use them as projectiles effectively?
Non war animals will run from enemies unless they're attacked. Even the mighty carp, if modded to be tameable, will run from goblins. Projectiles? You could try bridgeapulting them, but the fall might injure them.
6. Is there any way to move/get rid of/dump "owned" items that belong to dwarves who never pick them up (soldiers, nobles, dead soldiers and nobles)?
Dunno. Try giving the dwarf a cabinet in his/her room. I think when a dwarf dies though they stop owning the items, so you can always
wait apply magma.
7. I have fire snakes on my map, which I managed to catch several times with animal traps, but when I try to tame them, I get "error: Needs tameable creature item". I also try to extract fire essence, but then it says I don't have extractable vermin. Checking animal list shows them as "not tame". I also had one assigned to a cage, but it was never put in it. Why is this happening, and how can I extract/tame vermin effectivly?
Dunno. Did you tame small animal?
8. Been playing the map for 6 or so years with zero migrants (save nobles who "accidentaly" end up in my obsidian farm/chasm) due to their fear of death. Yet despite this, I have FOURTY NINE children and probably double the babies. My dwarf limit is 400. How on earth do I stop this, and how can I get dwarves to start arriving finally, because I need military replacements, practicly zero dwarves that aren't expendable/legendary >.<
You killed your nobles. That causes major fear for immigrants, they think your fortress is dangerous. My suggestion, find a noble with simple likes (say, who likes copper and tables) and just put up with him.
9. Where the hell is the underground river/water pool in "dwarf heaven" exactly? It's driving me nuts, and can't get reveal.exe to work, and I know where it is vaguely, but have yet to find the bloody thing.
Dunno. Try to dig in the middle of every 48x48 square, not necessarily perfect but odds are you'll at least find damp stone.