You can't "make it big" writing fanfic. I've been published on EqD 6 times, about as much as anybody. I have 570 followers and 56,000 views on fim-fiction. The most-watched writer is Pen Stroke, with 3000 followers and 125,000 views. Nobody knows me if I go to a convention.
Compare that to music or animation, where getting 100,000 views on a single animation would make you moderately popular.
Animation is a lot more work. It's best done as a team effort.
Music or voice acting is probably the best way to get famous--you CAN do it all yourself, though it's more fun to work with others.
But if you haven't already got one of those skills, you're behind the curve. I can't think of anybody who'se "gotten big" at something they hadn't already done for many years before joining the fandom.
In animation, comedy will make you famous.
In fan-fic, clop will get you a lot of followers quickly but will never take you to the top. Romance will get you a lot of followers quickly and /might/ take you to the top, e.g., SleeplessBrony. In the good old days of 2011, you could "break in" with a major long work. Now, you need to do comedy shorts to get a little attention. It's sort of too late to be "big" in fan-fiction--there's too much competition. No stories are going to become as famous as Fallout:Equestria, Past Sins, or My Little Dashie anymore, for the same reasons no writer will ever become as famous as Shakespeare. (He's not the best. He just got there first.)