The hard part is the battle system, but I have it all planned as I said and holidays are near, so if I don't go away for the 2 holiday weeks then I can stay at home and make it. The part with stealing pokemon, etc is not that hard at all :\
--EDIT1--
I had another idea that will be quite simple to make after the battlesystem is ready.
There will be a bunch of cities where there'S a place reserved to build a Gym, when you finish your game and become a pokemon master and your bored you have two options, either go to the Elite 4 for free, sit there and wait for random trainers to battle you (remember your a master :P) or you can go to one of these towns and buy a Gym, then you can go inside the gym, choose your pokemon type (you know, fire, water, etc or maybe even "only shiny" or "only dark" or even random types (you just use your normal team)) and then random trainers will come in, they normally will have one or two pokemon that are effecient against your type and their pokemon levels will be around the average of all of yours so that they can have a chance against you :P
Now, I know you're thinking "this guy has a lot of ideas but it is gonna be hard as hell to make that" you're wrong, the battle system is the main part, then creating random battles, etc is pretty easy :P
just so that you know CBS and CMS are the hardest things u ever get to make for a pokemon game, then you have mapping and events/triggers, etc that are not hard but take time ;)
so just give your opinion on both ideas (the one of being good/bad and the one of having your own gym/working at elite 4.
considering you can be those things I could later add more jobs like working part time at a pokemon center :D, be a cop :S, a thief, work at the daycare center, pokemon training (people lend you their pokemons so you can train them and then they pay you for it), etc
if you would like to see a job give ideas cause jobs and the decisions you take are gonna play a big role on this game. :)