best advise is if this is in a bar leave it in a bar. dont go using it all over the place. if you what to add songs get a external hard drive. The reason is that some thing like this is a work tool not a gimmic wich sounds bad but when doing busness its allways best to leave it were it belongs. you dont what to move some thing like this arround a lot.
virtual DJ is quite good esp at sequancing in songs. If it works with windows 7 and you not networking then chuck on a cheap version of windows 7. Its worth it. Forget linux and messing arround keep it simple.
The simplest tools are the best and for some thing like a DJ / Bar juke box wich i do have a whole load of exp at, the less rubbish on it the better. Allso make shure you are running virus protector on it and anti spyware and lock out USB for normal users and have a second admin account for enabling USB / DVD drive. this will keep the system in presitne condiction. Allso if you thinking of doing Vids from it you might what to enable tracking of the songs to download album cover ect ect but only allows this again for the second admin account.
you dont what to be rebuilding this things once you have 5000+ songs on it if it goes wrong. If you after juke box software as well let me know.
Allso another thing you could look into is remote admin of the system. this would be far better and that way you could make the box up and then hide it someware with a remote terminal to access the info and gubbings of the system. again this will make the main box you build a work horse. You could build a Ion based Dumb terminal so that you could remote in for changing stuff and at least if any one mession up the dumb terminal it aint going to mess up the main system.
. Or just build a £50 pc to remote acecss you need nothing fancy ...
Just things for you to consider.