3rd Gen Is this a good team for pokemon emerald?

I'm new to pokemon and was wondering if this was a good team for pokemon emerald. If there are any experienced players out there that could help me improve this team, then that would be great.

Swampert (Would like to keep)
Gyarados (Would like to keep)
Breloom (Replaceable)
Houndoom (Replaceable)
Magneton (Replaceable)
Gardevoir (Would like to keep)

Thanks.

For the most part it seems ok to me. Assuming you have the relevant party members when needed, you have something with a type advantage against every major opponent in the game (Gym Leaders, Elite 4+Champion, Team Magma/Aqua bosses), except for one, which is Drake, but you can probably beat him too (teaching Swampert and ice attack would help some). The one other thing you're missing is someone who can learn Fly, though I'm not sure how to fit that into your team without losing too much.

I think it's fine team. You might consider swapping up Gyarados for someone else, since you already have Water-type and Gyarados' movepool is pretty bad in Gen III. My suggestion would be either Ice or Dragon-type. Slaking is also fun to use, but not really beginner friendly.