You can play any of the worlds you want to without having any conflict with any others. There is an exception for worlds 8 and 9, you can only play one of the two. (Unless they have recently changed this)
If you start a game in world 10, it won't affect your game in world 1.
You'll start as a lvl 1 greenhorn in world 10, and your character in world 1 will be the same.
Each of your characters will be entirely separate.