As my 4a game draws to a close in year 7, mostly because I'm permanently at 10 FPS now (more to do with various animal explosions and opening two cavern levels than anything else, I expect), I've got some thoughts.
I do not believe that Familiars are working at this time. I have several different mages who would be eligible for familiars, and have posted changelings all over the place for them to interact with. They certainly used to work when they used Sprites.
In fact, the only time I ever got a familiar conversion message was when a magical baby was taken near my caged Vampire Lord. And I didn't get a familiar out of it.
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In 4a, clothing items were returned to invaders. I understand that this was to allow them to burn properly, but I'm not sure if that was worth the large number of items that it has added. Apart from the clothing items themselves, it also greatly reduces the need for making my own clothing.
As I mentioned in a previous post, we really need more things to do with lead. And some of the other less used metals too. Lead ammunition at the ammocaster would be top of my list, as lead hammerhead ammo would probably hurt quite a bit.
I have far too much stuff. Tends to happen when you're trying to keep your dwarves busy. More ways to use things up in useful ways would be greatly appreciated. I used to believe that the weight bench and the tavern would use up items for training, but it turns out that was incorrect.
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So far as funding, I pretty much made sufficient trade goods for everything I ever needed through a single archaeologist grinding up rocks. He produced a large amount of stoneware crafts. And when he found relics/treasure/fossils, he produced vast amounts of ruby light-sources and high value ballista bolts.
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I killed a Wyvern megabeast, sent it to the slaughterhouse, and raised it up again. It came back as a Red Dragon, which is fine, and I sealed it away behind a bridge for absolute emergencies, not wanting it to burn the place down during a Forest Imp incursion. It then promptly starved to death. I was not expecting a Red Dragon to be a grazer.