RE: downhaul specific
Boy, you've opened a can of worms on this issue. Not that it's not a fair series of questions to ask, but in the real world, people tend to feel so differently about the whole downhaul/outhaul thing. Frankly, a person's size and weight is really at the heart of what's right, especially under a variety of conditions.
From my perspective (70kgs), I like a lot of downhaul, and I secondarily adjust outhaul to suit the condition. But. I have to admit that I like flattened profiles, always with noticable positive outhaul. I'd rather rig a bit large and let the mid to top of range of sail design handle the extra power. I'm usually not too happy with a negative outhaul arrangement.
Notwithstanding my perferences, I know many bigger sailors that feel much differently, and as a result, they include much more pocket in the lower part of the sail, and may apply much less downhaul overall. Again, it's about preferences. Of course, different brands and models apply a whole different layer of concerns, and that must take in account the degree of sail structure (cam versus no/cam) and design intent.
Lastly, regarding the rigging process, I always use tools, such a winch for downhaul and hand cleat for outhaul. I didn't always rely on tools, but age has a way of limiting your potential and scope. It's kind of a brains versus braun approach in my mind, especially if your body can have issues.
Overall, experimentation is the key to happiness.