There are 2 articles on the Bella spinning site that should give you some help with understanding ratios: Spinning Wheel Ratios: The Single Drive Systems and Spinning Wheel Ratios: Double Drive and Accelerating.
Basically, for a thick soft singles, you want to spin at about 2 1/2 to 3 twists per inch. Use your largest whorl. Tensions should be set just so that the yarn will take up onto the bobbin easily but so you can pull it back off the bobbin through the orifice easily. How thick your yarn will be (the grist) depends on how many fibers are fed into each draft - the more fibers, the thicker the yarn, the fewer fibers, the thinner the yarn.
Now, if you want to felt the yarn after it's spun, the first thing you need to do is make sure that the fibers you are spinning will felt. Wool from different breeds of sheep felts differently, some is excellent for felting, some will hardly felt at all. For example, Merino felts extremely well as does Icelandic. Romney felts just so-so, and I've never met a Suffolk fleece that felted at all yet.
Felting yarn is fairly easy providing the fibers will felt in the first place. Put the skeins in hot soapy water and go at them with a toilet plunger (See the article on "Committing Yarn Abuse", then plunge them into cold water. Repeat as necessary. The combination of friction, soap and temperature change is what allows the fibers to felt. Once the skeins look just about right, whack them (while wet) against a flat surface to finish up - whack all the way around the skein. I would not recommend felting yarn in your washing machine as, with good felting wool, it can happen too fast and really mess up the skeins.