With making fan games like these, remember that the developers of the official games may send you a cease and desist. That's something you always have to worry about. I mean, look at Chrono Trigger Resurrection. That was taken down due to a cease and desist and it was maybe a month or so from being fully released. You have to always think of these kind of things in the long run. Do you really want to spend so much time creating a game, only to have it taken down so far into development?
And on that note...creating a homemade game (AKA Homebrew) could take a long time. Unless they're paid or they REALLY REALLY want to (which, in this case, most would rather go play Tekken GBA than make their own Tekken game for the DS), most people wouldn't put so much time and possible effort into creating such a game. In addition, most wouldn't even have the time to put into creating a game, as most people have lives to tend to. What about you? If you knew coding, would YOU have the time to create a game?
Also, don't even think about creating a full blown game by yourself with not much of a coding knowledge. Try learning a coding language, first. I would reccomend starting with Python, even if it really isn't what you'd want to use for making a Tekken game for the DS. It's an easier coding language and hey, RenPy (a python-based visual novel creator) makes it even easier to use. Which, it's a lot better if you start small anyway. Big projects like these loom to high over a newbie game creator's head and the projects eventually come crashing down.
And with sprites, music, and sound effects...Well, that sometimes doesn't mean anything. Sure, having those beforehand would cut down the creation time of any game, but you still have to put everything together. You may even have to edit the music so it loops. Or edit sprites so they fit within a small size-range that is befitting for such a game.
...Besides. If you took all the sprites/music/sounds from Tekken GBA, then why not just play Tekken GBA? You know? That's already using the sprites/music/sounds, it's Tekken, and it's a game that already exists and you don't have to create it.
