I like your proposed modifications! Here's a couple comments:
- As a tip, when making new levels, try to make sure that they're significant and unique/different from others in some shape or form. Adding new enemy types, challenges, or obstacles can help with this!
- Custom music is always a great way to make your game more unique and differentiate it - I'm excited to see what you make!
- Alongside what I mentioned for #2, I highly recommend putting some time into making custom backgrounds and art - this is a great opportunity to hone your skills.
I'm looking forward to seeing what you make!