Appledash,
First, Blender uses its own internal unit, called the Blender Unit, to measure distance. Torsten, who wrote the exporter has set the Blender unit to deal in meters. I'm not sure how he handles imperial measurements, because it's never been an issue for me, since I'm comfortable working in Metric.
Your goal of making Streamline SLSF passenger equipment is noble, but I'd submit you're probably not ready to do that just yet. I'd suggest you go to one of two on-line courses that teach Blender: James Chronister's high school level course (syllabus available at <http://www.cdschools.org/Page/455>; companion videos available at <http://4chron.home.comcast.net/~4chron/CDCADTutorials.htm>, or Neil Hirsig's college level course, offered through Tufts University, at <http://gryllus.net/Blender/3D.html>. While these were either unavailable, or maybe I was just unaware of them when I started Blender 6-3/4 years ago, I did start with a earlier version of the Wikibook <http://en.wikibooks.org/wiki/Blender_3D:_Noob_to_Pro>, and after working through the first 3 or four projects in the book, instead of making the models in the book began making rail related assets of similar complexity and incorporating similar principles as the project directed in the book. Which ever you do, a passenger car is a detailed and complicated project, and while I have no doubt that you could use the Frisco streamlined cars as your first project, I imagine that you'll find it much less aggravating, and you'll make faster progress if you learn to use the tool first.
Once you've mastered the tool, I'd start by making simple rail assets, for example, the step stool used at stations where there was a typical low level platform, progressing next to something like a baggage cart, and an small yard structure, like for electric distribution, or storage of explosives (fusees and torpedo signals were both dangerous, and stored in strong buildings to help keep fire away from them, and to control the blast if they should detonate accidentally). Then I'd progress to more advanced structures (the station at >your favorite SLSF locaton<), or the general store that stood at some crossing, where the crews, when they could make up an appropriate excuse would make an unscheduled stop and get one of Mrs. Baker's prize blueberry pies), then a freight car, and finally a passenger car. Once you have created these other types of content in Blender, the passenger car will seem almost (though not quite) trivial. BTW, if the SLSF streamlined cars you want to model were Budd built (and therefore fluted), my first passenger car would be a smooth sided car.
There are several blenderheads active in the Trainz community, you can consult if you run into problems.
Further, as far as video tutorials, there is a whole horde of them out there. First place is to check is the Blender website under the support item, <http://www.blender.org/support/> where you will find a link to official blender tutorials. Other tutorials can be found on Youtube, Vimeo, and other video hosting sites posted by Blender Sensei, Blender Guru, Blender Cookie, Ben Simonds, Blender Nerd, VScorpionC, and many others too numerous to mention here. But be advised these will be useful for learning about Blender, and not so useful for learning to make Trainz content. In fact, the only tutorial I know of that is of much utility specifically for Trainz is one by Jonathon Williamson (on CGCookie) about modeling a shipping container.
I would note that much of the content of Blender is not directly useable in Trainz (Trainz has its own lighting, rendering, and world settings, for example, and has no use at all for Cycles materials and nodes, unless these are planned for release in T:ANE or a successor, and have not yet been announced to the general community), and thus a good number of the tutorials are of minimal use, too.
ns
