All this based on a fine or communicative arts goal (not photo, fashion, ID, architecture, design management, etc):
A good portfolio would be between a dozen and 16 pieces, no sketches, no wips. More than 20 would just be tedious. You can tailor the content to their specificities, but it's not necessary - good work speaks for itself. Try to show breadth if you can, and the ability to observe directly - most schools are looking for somebody who can see in order to be taught, not who can be taught in order to see.
you won't get into any school without figure drawing, landscape/still life, perspective, and wet media (or at least some of these).
you won't get into any good school without the ability to create space.
you won't get into any great school without the ability (or potential ability) to create meaning.
"master copies" are "old fashioned", but "appropriation" is "hip." - this one i wish was not so true.
If a school cares about sketches they will ask for a separate book of sketches that will be given in addition to your portfolio - do not include them otherwise. Note though, a finished piece done quickly may be an asset.
"Severity" of process is very hard to measure because there's no such thing as a hard application or even a hard interview (if you're honest and attentive), it's all based on whether your competition is good. You'll be ranked and measured and assigned all sorta of qualities (accurate or otherwise) but at the end of the day, it comes down to the same stuff as most things : perseverance, honesty, confidence, and luck/talent.
You get out of art school exactly what effort you put into it. If you go in with the "I can learn everything on my own" attitude, you'll never learn anything from anyone.