IF your music files have been properly added to iTunes library then yes you'll end up with 2 copies of each. But before deleting, you should double-check that the songs are actually within the iTunes library. See How to transfer music to my iPod (& iTunes) for tips on using both LW & how to use iPod. Yes you can manually add songs to iPod but you need to see the tutorial 1st to see how!
The bitrate of lossless files depends "mostly" upon the particular song file. Yes some lossless formats might have some variation, but the point is how they go about reducing size without throwing away information. I've had an apple lossless file as little as less than 30% of original size & bit rate around the 300 odd kbps but mostly its about half size & bit rate varies between song. How hard the song is to compress equates to the size when compressed & the bitrate compressed at.

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Imagination is more important than knowledge. -- Albert Einstein
Only two things are infinite, the universe and human stupidity, and I'm not sure about the former. -- Albert Einstein
640 K [of computer memory] ought be enough for anybody. -- Bill Gates (1981)
The secret to creativity is knowing how to hide your sources. -- Albert Einstein
When facts don't fit the theory, change the facts. -- Albert Einstein
Religion keeps the poor from murdering the rich. -- Napoleon Bonaparte
The important thing is not to stop questioning. -- Albert Einstein
I know not with what weapons World War III will be fought, but World War IV will be fought with sticks and stones. -- Albert Einstein
"A composer is a guy who goes around forcing his will on unsuspecting air molecules, often with the assistance of unsuspecting musicians." -- Frank Zappa
"Tobacco is my favorite vegetable." / "May your sh*t come to life and kiss you on the face." / "Scientology, how about that? You hold on to the tin cans and then this guy asks you a bunch of questions, and if you pay enough money you get to join the master race. How's that for a religion?" / "Communism doesn't work because people like to own stuff." / "There are three things that smell of fish. One of them is fish. The other two are growing on you!" / "Jazz is not dead, it just smells funny." / "The creation and destruction of harmonic and 'statistical' tensions is essential to the maintenance of compositional drama. Any composition (or improvisation) which remains consonant and 'regular' throughout is, for me, equivalent to watching a movie with only 'good guys' in it, or eating cottage cheese." / "Remember there's a big difference between kneeling down and bending over." / "The most important thing to do in your life, is to not interfere with somebody else's life." / "Rock journalism is people who can't write, interviewing people who can't talk, in order to provide articles for people who can't read." -- Frank Zappa
"The music business is a cruel and shallow trench, a long plastic hallway where thieves and pimps run free and good men die like dogs. There's also a negative side." - Hunter S. Thompson
The shy can light the dull dark room with life when their eyes mirror their inner sunrise - LOTR