I am having trouble navigating the website. Where can I find schematics and part lists for a box that has 4 sid chips. Also, it seems like all the boxes I see other people make have traces inside of their boards. Are these pre-made or are you guys getting these done custom? I am really looking forward to making one of these so your guys help will be awesome!
Welcome aboard! 
What kind of trouble do you have?
The question you asked are all answered here: http://www.ucapps.de/midibox_sid_manual_hw.html
IMHO the questions you’ve asked are all answered here