When the area of interest is very big and the amount of data large, multiple PIX4Dmapper projects can be created for one area. To merge .tif files that are generated from the multiple projects, use an external GIS software like Global Mapper.
PIX4Dmapper can generate contour lines. For more information: Menu Process > Generate Contour Lines. However, it is also possible to extract contour lines using the DSM or DTM generated by PIX4Dmapper.
I am not familiar with Global mapper. MOBAC requires