No, you have unlocked the demo content of lfs, meaning you can only access demo cars, tracks and features.
You don't need to download anything else, as Silver posted you simply need to buy an S1 or an S2 licence. When you buy a licence you can then use that to unlock the S1 or S2 cars, tracks and features.
Follow the links Silver posted explaining how to buy lfs S1 or S2 and also what content is included.
In the host list (multiplayer -> display list of hosts) whilst you can see the s1 and s2 servers, they're listed in dark grey for a demo user as you cannot join them. They also have S1 or S2 after the host name in the list.
The server names you can join are in light/multi colours.
yes, go to single player then on the track selection screen hold down ctrl and you will see x and y before and after the track names, just click one of them.
It is very hard to lap a circular logo across that part of the skin as the front and top of the car are stretched differently, so getting it to line up and still remain circular takes a lot of rotating, scaling, lining up. as Silver said just keep at it and you'll get there.
As Scrabby said try get one that is fully ready as it will cost a fair bit speccing a standard road car up to rally spec. I would also say your better sticking to manufacturers that have cheap and readily available parts as chances are you will need to replace things pretty frequently
Keep a check on sites that specialise in selling rally/race cars, Ford Puma here on pistonheads fully specced for rallying at £2000 Link
5120x4096 will compensate for some of the stretching but it is not that accurate as on most cars the different panels are stretched by a different amount.
The most accurate way is using a standard 2048 or 4096 square template and using JazzOn's guide (Here) which shows all the values pretty much perfectly for each car.
If you are having problems seeing it then you can have a virtual speedo and gauges by going into options (either via the main menu or pressing shift+o in game) and change the option highlighted in red below and as you can see if you click the attached image it will display a larger version of your gauges.
There have been a couple of threads with people having similar problems, check the settings in your graphics drivers and make sure they are set to quality not performance, this seemed to be the cause for some
If you go into "My online car skins" in lfsworld then click the "1024 px" in the blue border underneath the upload skin button it will then download a .zip of them all.