Firstly, one of the things which turns people away from RMXP (RPG Maker XP) is that it costs $60. If you're not prepared to pay, you might want to stick to hacking. You do get a 30-day free trial, which gives you some time to save up.
Anyway, the advantages of RMXP are its flexibility and ease of use. Because you can see the raw code behind it, not just hex, it's much easier to change the actual mechanics, such as add D/P moves. Graphics are less limited too, since you don't need to stick to tight palettes. Mapping is more verstile, and usually easier. Eventing in RMXP is generally much easier than scripting in a hack.
However, you need to learn to use the features effectively. Mapping is only easier once you get to grips with the engine, and if you don't learn RGSS (the scripting language used), you can forget about adding new moves.
Also, hacking has two main advantages; firstly, RMXP games tend not to have move animations, since it's impossible to convert GBA or DS animations to work in RMXP. Secondly, if you have a flashcart, hacks are playable on an actual GBA/DS, but RMXP needs Windows to run.
For the type of game you're making, I'd recommend using RMXP. If you want it like Amethyst, hacking isn't going to get you very far.
Also, in a hack, you'd have to replace existing Pokémon to add new ones, while in RMXP, you can have as many as you want.
Oh, and if you get good at other things, such as mapping and scripting, you'll easily be able to find someone willing to help with spriting ;)
Anyway, the advantages of RMXP are its flexibility and ease of use. Because you can see the raw code behind it, not just hex, it's much easier to change the actual mechanics, such as add D/P moves. Graphics are less limited too, since you don't need to stick to tight palettes. Mapping is more verstile, and usually easier. Eventing in RMXP is generally much easier than scripting in a hack.
However, you need to learn to use the features effectively. Mapping is only easier once you get to grips with the engine, and if you don't learn RGSS (the scripting language used), you can forget about adding new moves.
Also, hacking has two main advantages; firstly, RMXP games tend not to have move animations, since it's impossible to convert GBA or DS animations to work in RMXP. Secondly, if you have a flashcart, hacks are playable on an actual GBA/DS, but RMXP needs Windows to run.
For the type of game you're making, I'd recommend using RMXP. If you want it like Amethyst, hacking isn't going to get you very far.
Also, in a hack, you'd have to replace existing Pokémon to add new ones, while in RMXP, you can have as many as you want.
Oh, and if you get good at other things, such as mapping and scripting, you'll easily be able to find someone willing to help with spriting ;)