I can answer the first one as I only use the LED Display with the lid closed.
The text is very clear, and I feel there is a ton of fine detail. I was looking at a Samsung LCD on my Vista Machine, and this thing is by far Brighter, Sharper, Better color, and not to mention Freakin' huge. The LED was the best purchase so far I think, it Turns the Air into a Desktop, then when I need to go the Air comes with me.
I bought the Mac USB Keyboard so when I plug it in to the back I gained another USB port. Apple has their crap planed out. Things I have pluged into the Display: MacBook Air Superddrive, USB Keyboard, and iPhone Dock. The Keyboard has 1 open USB slot with the other being taken buy the USB reciever of my Wireless Rechargeable Logitech Mouse. I am thinking of buying a USB Hub still but I do have one still open to connect a Camera, or a flashdrive.
I do have 1 COmplaint though, the feet on the MacBook Air are short, I understand why. You can't set the Air on the metal base of the Display like in this pic:
If you do you are covering up the vents of the laptop needed for cooling and since both are aluminum you get that metal scrape if you slide it on there. I think this is easily fixed if I have 2 wedges of some cool material I haven't thought of yet that I can place on either side of the display Foot and when they are lined up with the feet on the laptop they will give clearance enough to sit above the display foot and provide ventilation in the rear.