You are lucky in that there is a huge pile of information on the Internet. You might want to start with these sites.
Dome o' Foam
http://www.wx4.org/to/foam/a_rrcontents.html
My Espee Modelers Home Page
http://espee.railfan.net/espee.html
Southern Pacific Lines Forum
http://sptco.proboards.com/index.cgi
Southern Pacific Historical and Technical Society
http://www.sphts.org/
These sites will lead you to many others.
As far as maps and terrain are concerned, you can find track alignments from the late '70s to the mid '80s online from the US Geological Survey at MSR Maps at
http://msrmaps.com/. These are printable and highly accurate. If you are thinking of an earlier era, you should also visit Univ. of Cal. at Santa Barbara's offering of historic USGS maps at
http://www.sdc.ucsb.edu/holdings/caltopo.html
There were two lines that connected LA and Oakland, the Coast Line and the Valley Lines. The Coast Line carried most of the passenger traffic and the Valley Lines carried almost all of the through freight. The Espee was a very different railroad in, say 1975, from the Espee in 1985 and after, so your choice of era will make a huge difference in what and how you model. My recommendation would be to spend as much time as you can spare reading as much as you can find about the Espee in general. While you are doing this, you might take Euphod's implied suggestion to try a couple of smaller layouts to gain some experience in dealing with Surveyor.
You can find terrain only maps for Oakland and other parts of the Valley Lines on the DLS. The Coast Line is much better covered. If you do a username search for Fishlipsatwork you will find them. As far as I know there are no terrain maps for the Los Angeles Basin yet.
I've been working on this for a few years so if you have questions feel free to PM me.
Bernie