building your layout
Soonerfan,
Looks like you are getting some ideas well on the way. I don't think you would be able to get a pre-built layout with just some track on it. (unless your local hobby shop or model railway club will do it for you for a "small donation"!) Anyway, it's not that difficult to purchcase some track and lay it down on a board, hook up a controller and you're away! As for brands, I'm not fully up to it with all the brands etc that are available in the US, so that will have to be up to your "better judgment". With a 4 * 8 layout it would be better to keep it flat (without inclines) as 4 * 8 is not really big enough to have an incline that, say, rises, crosses another track (bridge) and then back down again. The incline would be too steep for a single loco to haul a decent load of cars up the hill, or it would slow down noticeably, or get wheelspin then race down the other side. Inclines should at an absolute max be no more than a 4% grade. ie a rise of 4" would need 100" of track going up and 100" of track going down. That's 200" That's nearly 17 feet of track (plus bridge length) just to go up, across a bridge then back down again. I run a 6% inline on Garahbara and I should not have done it. (I got greedy, and wanted a bridge/incline too, on a small layout). So think seriously about the incline idea.
I would also plan for the future too, if you intend to add some track later on. Think about the final layout, and put some turnouts in to allow you to extend later. It is not a good idea to rip up track once it is laid, especially if you have added scenery and track ballast.
Also consider your curve radius at each end of the layout. If you are using "fixed" track (ie curve pieces) or flextrack, make sure you select the appropriate radius to allow you to add a 2nd or subsequent parrellel track (inside or outside) the curve around your layout.
I hope these are some pointers to get you on your way and avoid the "what did I do that for!" syndrome some time in the future.
Good luck!