Welcome to the modding forums.
If you've downloaded the module system, and compiled it once to see how it works (make sure you've set the target to your own module name), etc.
Then for the windmill - you want to look at either adding a new trigger to module_simple_triggers.py, or extending the one that handles schools to also generate the extra prosperity for the village. The Native code for village schoolhouse is bunged - it doesn't check if a school house even exists, and only runs monthly. In my mod (and others I've seen), folks increase that happen weekly, and then also check for the mill (fish_pond), and apply a prosperity bonus based on that.
For the cattle growth - I'm a bit confused as to how to make it work properly.
Currently, there is a setup / world-creation script that sets each village as having between 7 and 32 cattle each, but within a few days they tend to drop to around zero. My understanding is that there is a trigger that fires every day or two that updates how many of each item each village and town has. And that its this trigger that would need to be altered to generate more cattle (the cattle are just a virtual thing - they don't really increase or decreased based on much of anything (maybe looting has a direct effect) - but mostly they just are recomputed every so often, and that's how many they have when you go look). I've tried changing the setup script to generate many more of them, and increase what seems to be the governing % that they'll have said item, but they still drop to abysmal levels shortly.
There are perhaps other modders who can answer this question with more light than I...
