For a first Paper Mario mod, this is absolutely mindblowing. The fact that you reused Chapter 5's Fearsome Five segments might initially come off as lazy, and while it certainly saved you time on map editing it's clear that you used that saved time to work on every other aspect.
The battles are significantly more difficult, which I wouldn't mind if it was possible to save inbetween battles without the enemies respawning. There's new enemies (well, they're really just heavily modified vanilla enemies I guess), some new items, and a ton of new dialogue. To counter the challenging enemy formations, the partners have been given a bunch of new moves which are just amazing really. Shoutouts to the Nuclear Bonk and the Triple Zest specifically.
With all that said, I still think more could've been done to separate this mod from the base game segment it's clearly patched over. You could've edited textures here and there, recolored a whole bunch of things (heck, maybe vertex painting would've been enough in some areas), changed some small details in the maps...
Still, this mod was a lot of fun to play, and I hope to see more from you in the future.