I like the main idea of this hack - but there are a whole lot of issues that need fixing.
LEVELS: You made some of the levels too flat and boring, and there needs to be more enemies. There are bad palettes, cut-offness, and some other issues.
OVERWORLD: It looks fine with its shape, but is far too bad. Cut-offness again, unmixing palettes, square edges, missing level tiles, and a lot more.
Now, you do have a good idea as stated, but I think you should scrap the hack in all - there is a lot of bad things in it. Now, about the music...
I have made an agreement: scrap the hack, and I will port the songs, even so make a few custom ones for the hack. When you make levels, there needs to be variety; more enemies, slopes, clouds, and some other things. Fix palettes that do not sore the eyes and prevent the cut-offness. Same for the overworld. Make decoration for empty spots, curve the land, and make sure you have fixed level tiles. I have provide links at the bottom for things you may want to look at.
How to Create Quality Hacks
How to Make a Good-Looking Overworld
Basics of Lunar Magic
The Next Steps of Lunar Magic
In-Depth Overworld Tutorial for Newbies (document)
Hope I could help you.