Interesting mod, with great promise and wondrous potential, but perhaps not for me. Looks great though.
I'm not really sure why players in DF are so dead-set on killing their nobles to make things easier, then go in and mod things like 'tougher farming' or steel making or what-not. The chickens thing, for instance, is certainly not a bug. As anyone with chickens can tell you, even a small amount of chickens will result in more fresh eggs then you and your family and your friends and anyone you know can eat. Likewise, farming enough food to eat is really, really easy. The problems come in, historically speaking, when farmers are forced to grow specific things, or all the same variety of one thing (see: the potato famine) which either results in not enough food for the farmers, or nothing that they can sell (See: Mysore, India during the 1920's/1930's). Its the mandates which make it hard, historically speaking.
That being said, if you try and make an industry based just off of exporting grown - not cooked - food, you will find it remarkably tough. But if you then cook and prepare it, it will become remarkably easy. Quality levels for prepared food result in prices that are a bit too high in my opinion, but...again, thats where mandates come in, to mess up farming, and steel-making, and what-not. But usually people just kill off the nobles...
Anyways, I like the mod. I like what you've done with it, and I think you've done a fine job. If I use it, I'll probably go back in and edit the changes to farming out, but I think you've done a wonderful job.
Best of luck, and good job on the hard work.
P.S. Regarding expansions, I would avoid getting too far away from your core principle, which is 'masterworking' the game, I think. Caste systems and religions get away from that. I'd stick to the core things which you have focused on, and try to make that essential enhancement as good as possible. If you -really- want to do religions or castes, I'd say just have it be an optional addon, or another (related) mod. If you stick to your core design philosophy, your mod could become an essential DF mod for many people. If you get too far away from that, it could just become another really great mod, because while almost everyone would want what you have in it already (or things like stone bins), the other stuff gets more into 'ordinary mod' territory. Which would also be fine. You just have to decide what your real goal is.