A DF fort should be well-defended. A good site will have a hill near a river.
Water can be diverted from the river to make a moat. It can also flow into the fort, to irrigate, to fill a cistern for drinking and washing, and to create indoor, dwarf-made waterfalls. Places for drinking should be upstream from the moat, and should be upstream from washing, irrigation, or anything else that might contaminate water. You can have perpetual running water if you have an underground lake into which you can dump. Use a floodgate as your sluice, and make sure it's backed by fortifications (ie., walls with arrow slits); these will act as a weir, allowing water in and keeping monsters out. Also, water being dumped in the underground cavern should go through another set of fortifications, to prevent monsters from the cave from climbing into your water supply.
The hilltop can be flattened or terraced, and can be used as farms for growing above-ground plants like strawberries, dye plants, or sun berries. You can turn the hill into a free-standing plateau by shearing the sides; then build fortifications and archer stations on top, and run your moat around it. The only way to get to the top of the hill should be from underneath, via your fortress. Your dwarves will be able to farm mostly in peace, at least until something flying comes along.