Welcome to the forums.
Keep LW's dwnld folder away from iTunes library. If you wish to import songs into iTunes, go to LW's Prefs>iTunes>Importing & tick the option box. iTunes will import the songs into its own library. iTunes will also show a LW playlist which is a list of all the songs you've imported via LW. This is purely a playlist.
The only thing about having iTunes import them at the end of their dwnlding is that you end up with 2 copies. One in iTunes main library folder & the other in LW's Dwnld folder. You can use one of them for backup.
I share most of iTunes library. I also share many folders from all over my comp. It's a personal choice about what you wish to share. If you'e worried about sharing, then do a search of the forum about sharing, legal, etc. Um I presume you have enough space to keep some iTunes music. You can share what you feel happiest with keeping in mind your HDD space situation.
Here's some hints on optimising LW:
A well set-up LW can start to automatically continue its dwnlding after it's settled down perhaps 2 out of 3 times you open LW. Optimising LW & Maximising Uplds & Dwnlds A (1st post only) & also Part B which is even better & last & least are search & dwnld hints. The latter one I've been thinking about re-writing for some time. That's just for playing it safe. eg- I show all speeds & qualities.