I'll try to answer what I know about the superleggera

1. There is a 20% premium over the Gallardo Coupe. The premium covers a number of lightweight items made from carbon fibre (centre console, door trimings, roof (i think), spoiler, mirrors, rear bonnet with clear plastic), it also has straight through exhausts, light weight rims, more sportier seats, and a different steering wheel. It also only comes with e-gear (i think)

2. Lamborghini are quite secretive on what's to come in 2008. They have promised to release a new car every year tho. So expect something to be released next year, who know's what tho. Something that might be worth looking into is a rumoured release of a GT2. Lamborghini Chicago are having an event for the launch of it.

3. It's been said by the CEO of Lamborghini that they have already sold the numbers for 2007. 375 were allocated for the year and they've sold over 400.

4 & 5. Sorry, can't help there as I'm from Australia. Check your local dealers.