Bottom line is going by volume, time, weight, etc. will simply get you to a ballpark area, then you fine tune based on taste, texture, etc. How much coffee you use depends on the machine (group/shower screen design, basket depth), grind fineness, etc. Feel free to try the 2 oz. in 30 seconds type guidelines to get started.
Get a decent scale that weighs within .1 gram increments. A few tenths in either direction won't make much difference, but .5 grams or more definitely will.
The only difference between a latte and cappuccino is air. When texturing for a cappuccino just use less milk in the pitcher and apply more aggressive steam/air to allow it to expand about double the volume. If done in a decent manner it won't be dry/bubbly unless that's what you want. Ratio-wise a cappuccino will be about 50/50 on the steamed milk/froth volume and a latte more like 80/20, but if textured in a decent manner the end result for either should be silky smooth and not really separated.