New to Sonos - A Few Questions

[FHB1]

Greetings Everyone. This is my first post. I've been reading about sonos for quite some time now and it seems like exactly what I've been looking for. Today I decided to take the plunge and I ordered 2X Play:5 and a Bridge. I can't wait for them to arrive! In the meantime, I've been reading as much as I can so that I can hopefully have a smooth setup when my sonos equipment finally arrives.

Before I get to my questions, here is my computer/network setup that I'll be working with:

Macbook OS X 10.6.8, Airport Extreme Base Station, Western Digital My Book 1TB external drive connected to the AEBS via usb cable.

I have two iTunes libraries on my WD hard drive that I currently access wirelessly with my laptop. One of the libraries is over 500GB and contains way too many files for sonos to use. The other library consists of around 8,000 songs of my favorite music. This is the library that I plan to use with sonos.

One question I have is, can I have sonos only access the music from my smaller iTunes library and not have it access music from my larger one, or will sonos automatically try to retrieve all of the music on my external drive? I started getting nervous about this because I read that sonos only reads "root level folders." What exactly is a "root level folder." Do I need to worry about this?

Another question I have is regarding importing my iTunes playlists into sonos. My iTunes .xml and .itl files are located on my laptop and all of the music files are on my external drive (in two separate folders). If I set up sonos to access the music files on my external drive, I am assuming that sonos will not be able to access the .xml and .itl files that are on my computer so that my smart playlists can be added. If I have my iTunes set up this way, will sonos be able to read my smart playlists? I have read about this in the forums, but I haven't found info regarding my particular iTunes setup. I appreciate any help you can give me with this as I really don't want to loose my smart playlists.

Please pardon me if these seem like noobie questions. I'm just very excited for my sonos system to arrive and I'm trying to troubleshoot ahead of time in hopes of a smooth setup. I appreciate any answers that you may be able to provide. Thank you!