Good Fit Guide
Regarding cut, the jeans should be slim in the thigh and straight or tapered from the knee down.
Go with your waist size and stick with straight leg or slimmer. Reduce down slightly on the waist size for a slimmer fit. The jeans will stretch.
When it comes to breaks due to gravity, most people don't want more than a few, as shown. Some people aim for more breaks, this is called "stacking". Ultimately the number of breaks is a matter of taste. Depending on the style of the jeans and rigidity of the denim, you can get away with bunching further up the leg. Since jeans are very versatile and can be fit with numerous styles, this varies.
Length can vary if you plan to have turn-ups on your jeans. Turn-ups can vary from 3-12cm depending on your style.