Not going to lie mate, it is HARD. That being said, it is doable, and a lot more rewarding. Just choose one thing to learn/focus on at a time, make yourself a test ROM you can try new things on. Slowly but surely you'll get the hang of it.
Hard as in it's all on you, and your time only. Sure, progress would go faster having a team I suppose, since you can have one person focus on each task, but this could get messy pretty quickly. Plus, as it's already been said, if you've got a team you won't just lose a bit of creative control - you lose all of it. Nobody, literally nobody, would work on a hack having everything dictated exactly as things should be when they might not even like the idea therefore won't be motivated to do it, plus there's the chance of clashing over ideas. If you go it alone, you can do what you want the way you want to do it =)
EDIT: Slightly off topic (?) but still a good point to make imo, especially when alone ~
Hacks don't happen overnight. Sure, you can make some types of hack quickly, but that depends on what kind of hack you want to make - the faster-progressing ones being things like 386 patches or increased difficulty. If you want a hack with a new region/story/characters/the works, it's going to take a LOT longer. The comments I'm making next are referring to the latter.
For example, you don't need new tilesets. I don't care what anyone says on this subject; you don't, you can make a perfectly decent game using original tiles. Graphics don't make a game. That'd cut the development time, as would things like keeping original sprites and features, etc. Sadly, if you do want those kinda things, gotta put time into it. There aren't any public tiles for what you wanted in your map? Better learn to draw them yourself then, etc. Development time really does depend on what you want to do. You need to know that it could take over a year, and you need to be okay with that. =)
