I'm into semi-scale as well, got a k4s, 0-6-0 b6 switcher, gp9 ,and a couple others, those are the basics for any Pennsy fan. I have The History of the Pennsylvania Railroad by Timothy Jacobs, good read, lotta pics, and another good one, the name escapes me at the moment.
Lotta good Pennsy videos on youtube as well, just go there and type in "Pennsylvania Railroad" and its a feast for the eyes to see and hear the Pennsy in action.