You can only preview as much as you have downlded. Let's face it, even streaming audio/video means you must 1st downld a certain % before you can use it.

LW is legal. But how you use it is up to you. You are downlding what other people are sharing. If it's copyright material then the onus is on you to decide whether to downld it or not. Not all files are copyright material.

There is no legal free downlds of copyright material. The legal status depends on your location/country, etc.