Advice to start ROM hacking (Pokemon Emerald)

[Kresuu]

First of all, apologies because I've seen "newbie posts" around and I'm sure this question gets asked often, but it's pretty straightforward. I'd like to start making my own rom of pokemon emerald, and I really don't know how or where to start. I have more than enough time to dedicate to learning all the things necessary. I chose emerald for two reasons: it's my favourite game, and so far it seems like the "easiest" on to dive into for rom hacking. I would like to know what the best tools are for things like adding a new pokemon, creating new map areas, messing around with shiny odds, changing experience given when defeating a pokemon, the list goes on. I'm sure some of these are more complicated than others, but I'm here to learn. I might be wrong but I've seen two main ways you could go about this, which are binary hacks or decompilation. I am really interested in both so I don't mind which one to go first, so as long as I start building up knowledge. I am not new to programming (mostly C#) but I am completely clueless about things regarding binary.

Either way, thanks for reading and I appreciate any advice I can get, have a great day!