You're using Gecko, right? You have to specify your launcher because different launchers use different properties to get the hacks into Brawl. Riivolution for example uses .xml files that account for a specific file configuration.
I don't know about you but I find model importing fun in general. It gives you such a nice feeling when something you created and rigged yourself works in Brawl even though it could use a little more touch-ups. Nothing beats the feeling I get when I see my successful import beating up Wario in Brawl.
Just a heads up but if it comes with a FitMotionEtc. pac or a FitCharacter.pac (w/o any numbers) it would be wise to be put those in as well as they are often intended for the mod to look its best. Most hacks don't come with these, but these change a character drastically (some even change a character's moveset) and they aren't one-slot meaning they will affect all hacks associated with the aforementioned character.
Well if you're planning to make re-textures or recolors then yeah.
But all the work is done for you if you mean just using the hacks, the only thing you need to do is copy and paste the .pcs and .pac files to the corresponding folder.
No, 00 is original, 01 is red, 02 is green, and 03 is blue. It's like that for most characters except some characters colors are already the original ie Mario doesn't have 01 because his original is the red team. But I see you get the idea so yes you do that.
Me I have the ability to hyperfocus and is always able to rig an entire model in one day (though it takes a half hour or so; I never pay attention to the time). But there are days where I want to do something else so I don't touch modeling or Brawl hacking.