Basic track tiles
It is likely that about 20,000-30,000 separate images will be needed for all the game graphics. This is a huge number but through smart use of 3D software and automation making these graphics is comparatively simple. Since starting the FreeRCT project I have been working on several projects with similar graphical requirements to FreeRCT. These projects have let me work out streamlined workflows for creating this type of image; my last major project was an extra zoom level graphics set for OpenTTD. If you are interested you can read more about that project at these blog entries: Making a Massive Graphics Update, Moving to 3D, Automation, The Finished Product.
The very first shop
So far land, cliff/foundation, water, path and path support graphics for FreeRCT are made (although there are some technical issues that still need working out). The next big challenge will probably to make templates for track rides, in particular the track pieces which stretch over more than one tile.