I'm... not sure how I feel about the tin things. On the one hand, I really, really, really love the concept, and you obviously put a lot of thought into it. On the other... magical, ridiculously-durable droids that cannot be hacked or reverse-engineered feels a bit sparklypoo to me (yes, I'm aware that we already have bronze colossi in actual DF canon). Also, you may have put a lot of work into their backstory and behaviour, but the tinmen themselves are a bit too cipherous in their inner workings for my liking -- they kind of feel like fairy-tale creatures powered by nondescript 'magic' (or to paraphrase Futurama, 'It Just Works') than anything else. Yes I am aware that this would be a drop in the bucket compared to all the random sci-fi-fantasy bullcrap we already have floating around, but this seems to be particularly-egregious to me for whatever reason, probably because people have actually tried to determine how it works and largely failed. You described their inner workings in minute detail, but it still boiled down in the end to 'we have no bloody clue how it works', which tends to read to me as an admission of ignorance on the authour's part. You, at least, had better know exactly how these things work, even if you're not telling us in their backstory. End opinion: Approve, but tread lightly, 'cuz you're in sketchy territory. Also, you might wanna make them into an SCP if you can, because that's the vibe I was getting from them.
As for the gnolls... I don't think I can object to the inclusion of any sort of sapient based on hyenas, who are (in true, objective, indisputable fact) the badassest and most adorable non-amphibian animals to ever grace the African savanna (lions can go straight to hell). I kind of came away from your writeup wanting more, though, particularly with regards to their biology, which probably could have been more in-depth (you didn't touch on their psychology much at all, for example). Also, I reeeeeeeally don't like how over-the-top evil and brutal they are. End opinion: shows promise, needs work.