I love all of these ideas! I know everyone keeps saying this, but I still really want horses, too! With horses and/or other livestock you could have farming shows/rodeos which could maybe award simoleons/trophies to the winner.
I think the two ideas are similar because I'm imagining this as a "Homesteading" EP which of course means living self-sustainably (food, water, energy, etc.)
I agree that most of these ideas seem dependent on a Seasons Pack first. With a seasons pack it would be interesting if your plants didn't grow properly during a dry-spell or you couldn't collect rainwater. Canning would also become necessary if you were unable to garden in the wintertime.
With off-the-grid type items like windmills and rainwater basins I think they should reduce the amount you have to pay in bills, but not eliminate bills. I'm imagining they'd still have regular expenses like a mortgage, taxes, insurance, etc.
I've also always wanted wheat and milk and a way to produce flour/bread and dairy products in game. Harvesting eggs would be super cool too! Additional recipes to go along with the new harvestables would make sense. Also agree that canning would be fantastic.
Lastly I would be SO thrilled if you could set up your own farm stand on your home lot. Maybe it would just be an interactive "display" item that you plop down and then place produce/eggs/canned goods on it. Townies could visit your lot and leave money in a jar for your items. I guess it's sort of like Get to Work in the sense that you own your own business, except it would just be a small item on your home lot and your sims don't really need to "work" there. They would just need to place the items for sale on the display and collect the money every once in a while.
I'll admit that I'm asking for a lot here, but these are my dreams for my current household. They're living as farmers and these capabilities would just revolutionize the gameplay in that house.
