Your defiantly on the right track but there are a few things I'd do differently. First learning the keyboard shortcuts will improve your workflow ten fold and will reduce any errors by visual moving each tile into the correct position.
I'd make all your tiles the same sized square, rather than the street corner a square and the straight a rectangle. That way the grid size in Leadwerks will be all the same for each piece.
After setting the origin to the cursor, if you click 'N' it'll show you the objects position in blender and you can set XYZ to 0. The model's origin will go straight to the centre and I'd export from there. Do that for each tile, I think FBX will export it's offset from the world origin and can stuff up tiling in Leadwerks.
I wouldn't scale on export (that's probably just my preference though) I would scale the mesh in blender to the size I wanted, make sure the objects scale is applied in blender with Ctrl+A. Sometimes odd scales can cause issues.
If you have consistent tile sizes and consistent export locations there shouldn't be any problem in Leadwerks. At least not with geometry lining up.