Main Street Station was at the start of it all. I built than around 1998, a few years before the days of everyone having a digital camera and pictures of everything on the internet. I had a heck of a time getting all the views I needed to kitbash the model. My biggest problem was that with all my books and pictures and the limited amount on-line back then, I couldn't find a view of the east side face of the clock tower so I didn't know how to do the upper window on that side. I bought all the parts two of the "standard kits" plus a bunch of parts at my local train store, but I couldn't do that today as they mostly sell finished models (I guess built in China with cheap labor).
In 1999 I had the opportunity to go to Disneyland 4 times in one year and took extensive pictures of Main Street on FILM and then digitize over 1000 negatives and then formed composite pictures of the various blocks of Main Street in Photoshop. I had a 1 megapixel digital camera but the images were not good enough to use so I kept with the SLR and film.
The paper model of the castle are from http://www.disneyexperience.com/services/models_index.php
and the Haunted Mansion is from Haunted Dimensions. In both cases I took their original versions and rescaled them to HO in Photoshop before building.
I'm pretty sure the train is a Rivarossi Reno (with Virginia and Truckee on the tender). From what I gather, they are no longer in business. I liked the look of this engine relative to the Disneyland E.P. Ripley. It has the motor in the tender which keeps the "engine" from being too bulky.