As I understand it, as long as you use polygons that aren't curved like NURBS curves in sketchup, then blender can convert them to triangles automatically when exporting to CrystalSpace. So don't make everything in tris, because bigger polys can be easier to texture and then be converted after texturing to tris. The only time I use exclusively tris is when I don't know how the automatic change to tris will work, for example if I have a quad that isn't flat, but bent, and I want the tris to split the quad across one diagonal and not the other, then I manually divide the space up the way I want it. I know I'm repeating what Niko said to a great degree, but I'm trying to say the same thing in a different way.
It may interest you to know that there is a plug-in for blender that lets it import SketchUp files. This way, If you are more comfortable modeling with SketchUp, you can model in SketchUp and then import with blender and work on textures from there. I haven't tried out the plugin myself, but it may work for you.
Also, IRC is an effective way of conveying meanings and teaching easily and quickly, and it really would be a help if you could make it on. You can use
http://webchat.freenode.net/ to login, and the channel which botanic mentioned earlier is #planeshift-citycontest.
Hope to see you there.
Interiors would mean both, if you like. The best place to start may be getting practice doing possible guildhouse interiors. They ought to follow the external structural patterns of the buildings, ie. the same angles in wall corners and several floors.
-Zweitholou
(p.s.- If I'm inaccurate as to any of this, please, someone who knows more than I, correct me.)
