First time creating an hack rom

[Lesaath]

Hi! I'm Lesaath, I'm new to creating hack roms (except for a really bad sapphire one I did like 8 years ago) but I played a lot both GBA/NDS and RPG Maker fan games. 

What I want to do is creating a game/rom based on the Sinnoh of ~20 years before the D/P games and you play as a young Cynthia that starts her adventure.

I have a more clear idea in my mind (so if needed I will post more) but basically is that, you start in Celestic Town and then it will be basically a normal pokemon game of the main series.

Now, the reason I am making this topic is that I don't know how to proceed to make things well. First of all I'm divided into trying to work with RPG Maker or NDS Roms (even because Idk how much you can edit with NDS tools).

 

A little advice on what should I use and what is the best way to proceed for the project would be really appreciated ^^

Thanks to everyone that will answer and sorry if this is not the right section ^^"