If you copy the plans at Kinko you can put the master over the copy, hold it up to the light or on A window and double check that the copy is at 100% of the master. If not have them make up another set. One day I had them do it three times because the new operator of the machine didn't know how to set it correctly. They may not like it but they have always done it. That's why I use there service.
That thing about cutting or sanding to the inside or outside of the thick lines has been something I have always wondered about. In my case I just choose how I want to do it and stick with that way all the way through the kit building stage and it always works out well.
Have fun with it, that's what building is about.