You can make a lot of complicated shapes with one dodging tool just by moving it higher/lower, back and forth and rotating it in relation to the light. Use your imagination to visualize the shapes you can make with just one tool this way. Reinhold's brochure gives some basic examples of shadow shapes you can get from one tool.
For exposure, I always think of my dodging as a percentage of the entire exposure (e.g., dodge that flower 10%). For dodges that require moving around a lot during the dodging, I try to estimate the total percentage that is being dodged overall. I find, that unless I've overexposed my negative a lot and there's a lot of shadow detail I'm not using, that a 15% dodge is about all I can do without affecting the blacks adversely when dodging a dark shadow area.
I have a set of different size round and square/rectangular dodgers that I made myself. This I add to regularly with special shapes for particular applications. I use my hands a lot too. Sometimes I have so many dodging operations that it becomes a real choreographed "dance of dodging" during the entire basic exposure. Complicated dodges need to be "rehearsed" and are a real creative part of the "performance" of print-making.