Can I not submit the supplemental portion of an application? Is it okay if Columbia or other colleges only receive the required common app portion?
Sure. But your application will be considered incomplete and will not be processed and you will have wasted $80.
It depends upon the college. If the questions are required, then they are required, and your application will be incomplete without them. If they are optional, then you can choose not to complete them, and your application will still be considered. The Common App lists what is required and optional for each of your target colleges.
Follow the directions.