Developing/Designing a Pokemon Game...

Working on a new game, though the amount of thought I want to put into it should mean that it will be quite time-consuming, and should take several years to finish.
The game is going to include all Pokemon from Red/Blue/Yellow up through Diamond/Pearl/Platinum, and all Pokemon will be available, some through in-game trade.
In addition, I'll be putting Museums in every town that will shed light on the town's traditions and history.
For example, the museum I'm planning in Viridian should explore the sporadic reappearance and disappearance of Pikachu in Viridian Forest, how Blue came to be gym leader of the Viridian City Gym, how Viridian was previously a headquarters for Team Rocket, and so on. In other words, the museums will contain actual content.
The world I'm attempting to create should have a great deal of depth.
I'll try to explain things that weren't explained in previous Pokemon games, such as how bite became a dark-type move and how the elements steel and dark suddenly emerged. I'll try to explain why the trees that the game developers designed as barriers have not been explored.
In addition, I hope to incorporate the Orange Islands, as well as Johto into my Kanto-based game, though Hoenn and Sinnoh will stay out of the game, as they don't have quite as much nostalgia for me.
It should be very complex, and the time that I'll have to put into it will probably be pretty significant.
I'm not quite sure where to begin. I don't know what programming language is best, how to develop sprites, and so on, but I'm sure I'll pick up on this stuff as soon as I have a more definite idea of the plot, then a very specific eye for details.
I'm designing several cities as well that were not included in the Pokemon games, and as I said, I'll also be interpreting the Orange Islands.
Two things unique to this game:
1. Legendaries are not found through in-game events. Most of them roam tall grass completely randomly, and the odds of running into one are 'nil, (almost as small as running into a legendary Pokemon,) though some of them are placed in specific places, and are obtainable through a TON of effort. (Moltres, Articuno, Zapdos may wander tall grass, though I may also put them on islands in the Orange Islands; Raiku, Entei, Suicune will wander tall grass along with Latios, Latias, while Manaphy will wander the seas... Celebi will be found in trees spread throughout the game (I intend to incorporate the trees I use as barriers as homes for Pokemon, and maybe include animation similar to the trees on which you slather honey in D/P/Pt.) I'm not sure where I'll position the other legendaries, though Mew should be in newly-created ruins somewhere far out of the way.)
2. You do not start with a Pokemon. Unlike in previous games, I don't intend to take it easy on the hypothetical player, and I intend to take somewhat more of a Safari Zone approach to catching Pokemon. All starters from previous games will be catchable... I just like the idea of having to level up a Pidgey or a Rattata, then earning the Squirtle, Torchic, Chikorita, or Piplup that you got the luxury of obtaining early on in previous games.
Also, I intend to diminish the number of HMs required in this game. I'll include Fly and Surf, though Flash is probably going, and moves that necessitated HM slaves in previous games such as Strength, Flash, (TM later on... thank goodness!) Whirlpool, Waterfall, Cut, Rock Climb, and Rock Smash.
The game, as I said, should take a long time to finish, because I also intend to include more restaurants and businesses in the game for the sake of realism.
Anyway, that's the plot. Any advice you can give me would be great as to what programming language would best serve my purpose!
I'm exploring Python, then hope to advance to OpenGL, though I'm not sure if those are the types of languages I need to use.

Features:
More Realistic Stamina Base
All First, Second, Third and Fourth-Gen Pokemon Can Be Caught In Game, from Bulbasaur to Arceus!
Larger Cities
More Depth
More Challenging
Bigger Map, Including Everything Adaptations on Kanto, Johto, and the Orange Islands
More To Do In Cities, Including Museums with Explanations on and Homages to Previous Pokemon Games
HM's cut down to Fly and Surf to eliminate the necessity of HM slaves
Ability to Buy and Manage One's Own House

Current Projects:
Map development, plot development, and learning programming language

Should probably make that post readable.

Thanks! Writing big text walls is a bad habit of mine.

Hmm... only one response. I guess I'll post something more concrete when I have more details on the game, though the plot hasn't fully worked itself out yet. I'll probably have Team Rocket resurface under somebody else's leadership, and possibly incorporate Team Aqua somehow...
Anyway, more details on the way. Don't know why the lack of response, but I've got a friend working on the music for the game, and between writing and learning the guitar, I'm developing the maps and plot. I'll post it up when I have more details. This game probably won't have a title until I've figured the plot out or actually develop the game, since that's how most work titles itself.

Lack of response is due to lack of content. You shouldn't create a thread before you start working on the necessary resources...

It seems to me that your best bet for a development platform would be RMXP, but you'll struggle if you don't know how to use it. Game Maker is more flexible, but you would have to program almost everything from scratch, which would be near impossible if you don't have experience with the program.

Go for RMXP and see if you can pick it up..