Thanks for the feedback (You even made a video
I've got to admit that the section with the sky pop was a bit experimental (and the sky pop is a bit buggy in SMBX).
I've added the codes to npc-290.txt and I changed the first section, but I just removed some enemies and raised the roof. Problems 3 and 4 still aren't solved, but I think it should be better now. I don't really know how to solve these problems without deleting the whole roof and deleting all the enemies, but that would be boring.
The warp is also fixed, thanks for the tip.
Once again, thanks for the feedback, it's appreciated.
I'm also glad you like the music