1.) is not a significant modification for the final submission. Check the D2L discussion boards for a range of solutions to this problem, most likely you have not set your background images to have their sprite renderers on the background layer see: Project 2 - Level Setup (Part 10 of 17) - SS23-CAS-117-730 - Games and Interactivity (msu.edu)
2. this will work as a significant modification as it is a unique level.
3. each power up you make can count as a significant modification. Better if you also make levels that exemplify the use of the power ups.