To simplify there are two types of muscle fiber white/fast twitch that are your speed /strength muscles and gain size but not as much as the red/slow twitch endurance muscles.With weights you train the white with reps of 3-6.You also develop the white doing anaerobic sprinting activities.How much size you develop training these muscles is dependant on your genetic percentage of white fiber.Moving to the red fiber the percentage of which also varies genetically rep ranges of 8-12 with weights best develop these fibers size.There are two drawbacks to this though first much of the size comes from development of so called satellite cells which provide bulk but no real functional use (at least that was known a few years ago when I use to read up on all this)second bulking up the red cells reduces their aerobic capasity and they are the primary endurance muscles(so there is a tradeoff between bulking them or building endurance in them).
Having said all that I think your focus should be on developing the white strength fibers with a few effective compound exercises.The "big three" squats,deadlifts and bench provide a total body workout with just three exercises.If you want to drop the legs and focus on upper body I would replace squats with clean and presses.You could work a few sets of these three exercises into your overall routine in ways I mentioned in the previous post but the idea here is to reduce the volume to a few heavy intense sets of highly effective exercises thateach work multiple bodyparts.