So I think I've finally gotten an idea of how to tackle maining. As of right now I plan on sticking with Mario, but I've always liked the idea of Dr. Mario (a stronger Mario), so I plan on using my knowledge (or soon to be) of Mario to get better with the Doc. As while they have differences, they both still share similarities. And I can work off of that.
In regards to other mains (like secondaries), I have ideas for what to do, but for right now I plan on getting good with Mario/Dr. Mario and then working on the others. Currently the only non-Mario main I'm trying out is Mr. G&W, though the others I've been interested in are Pac-Man, Toon Link (especially for Little Mac players), ROB, Miis (specifically Gunner and Brawler), Duck Hunt Duo, Bowser Jr., Olimar, and Pit/Dark Pit.
As of right now it's pretty much learning how they work, how the moves work, basic combos, and going from there. I also hope to learn the community. Since doing it alone is not the best thing for someone like me to do. Other than that, not much else.