A Rack System? WTF! It Defeats The Purpose Of It Being A Cabinet, But Good Suggestion. And Don't Get Technical I'm Only Eleven!
Well, 1U just means that the box is 1.75" tall and about 19" wide. (2U would be twice as tall, and so on. 4U, like the computer I'm currently assembling for myself, is 7".)
Ever seen a server rack cabinet
? You can get them from little short things for audio equipment to about the size of an end table all the way up to ceiling-tall. (Things besides servers use cabinets like that too, such as audio mixing equipment
can probably explain it better than I can.
Oh, and a punchdown jack is basically the kind they usually use for putting network/phone jacks in a cover plate in the wall, like the cover plates they use for outlets and switches.