Hi, thanks for reporting the crosswalk bug! I will look at it but it is most likely caused by too sharp angle between road segments and it would be too complicated to fix (but I will definitely put it to my backlog).
You can already add your own models as part of the distribution is LodCreator tool which imports OBJ models and converts them to engine native OFR format. You can also create "textures" directory alongside the OFR model and you will be able to load textures there in both LodCreator and engine. Unfortunately shader selection is currently very limited but I plan to add PBR materials in future.