Thinking about Laptop system - Newbie Questions

As an old timer (listening to 50% vinyl/50% CD), all this music server stuff is very new to me, but I am somewhat computer literate. I was thinking about building a nice little laptop based music server. Thinking about either a Logitech Transporter or Squeezebox Duet with separate DAC. I have a wireless router close enough to the 2 channel system so I can go either wireless or Ethernet.
Laptop is Toshiba with 4 Gb RAM, 340 Gb HD. I would use a stand-alone HD to store music.
So, I have a few questions: Transporter vs. Duet/DAC?
What format to store music? WAV, FLAC, etc.?
Can I still use the laptop while playing music?
Any other helpful hints?

Sorry for all the newbie questions. I am doing as much research as I can before I jump into this.

Thanks for any info.