Okey dokey, lets take it step by step
1. You can use skins in demo, believe me, i was a demo racer for more than a year and a half. Your skin needs to have the name XRT_"putherethename" . The _ has to be there ! Than put the XRT_"whatyouwrotehere" to your LFS/data/skins directory. Load LFS, go to the garage , select XRT, go to the colors tab and then click on Texture name . Now you only have to select your texture ! In the demo you _can_ use skins, but you can't upload them to LFS world
2. If you buy S2 now for 24 pounds then you'll have to pay 12 pounds for S3 when it comes out. If you will wait until S3 comes out then you will have to pay 24+12=36 pounds for S3 =]
3. Please use punctuation as it will be easier for people to understand you and so they will help you a lot more!
Sorry , i don't know where to find a carbon fibre hood, try MasterSkinnerz, or search for it on the forums !
Hope I helped a little bit, and good luck with your future skins !