2D Platformer

I think that your modifications are headed in the right direction. I do have a few questions:

1. How are you planning on making your levels significantly different from each other/unique? The best advice that I can give you in terms of level design would be to make sure that each level has some sort of unique identifier. New types of challenges, enemies, obstacles, or powerups can massively help with this. Putting some time into playtesting and differentiating your levels (to figure out, from a player's perspective, how the level plays) can also give you some direction in how to design things.
2. Will you be making these art assets yourself?

Best of luck, I'm looking forward to your finished product!