The Topaz championship is the most famous gempukku ceremony, not the most important.
Depending on your setting (1st ed, 4th ed, 5th ed, homebrewed) it might be different so I will write here some general perception about the tournament.
While this ceremony is a grand event for all to see, most gempukku are actually done before or after, in the privacy of each clan/family. So depending on your family's tradition, the Topaz championship might be a formality or a sine qua none condition. A few examples can be found (Shiba needing to write an essay, Shosuro needing to blend in a crowd, Hida needing to defeat a shadowland creature) if you dig into the literature.
Famous, means that for clans that favour glory and honour, this is of particular importance. For the crab, a bushi in a tournament is a bushi away from the wall not fulfilling its duty. Depending on the current political and economical situation of the Crab, the presence of one of its bushi might for example be a waste of resource, and thus they would send their most useless child unattended. On the other hand, a Kakita duellist, doing the competition in the city of its academy, will be the brightest and most skilled exceptional talent available. It all depends on your clans willingness to shine in front of the high rokugani society.
RP is first and foremost about your player's enjoyment of the plot/setting/universe. If they do want to feel like heroic youth, give them this role and go for an heroic setting. If they like gritty, dark, horror kind of settings, you can make the whole tournament an obscure plot driven by an evil entity. It all depends on you and your players playstyle.
One thing to note though is that if you are using the 5th ed beginner's kit, the setting is quite undefined. The fictions/free pdf will give you clues but nothing really structured. So if you want to stick to the official version, be careful to explain too much as the official stories and books might go in a different direction. In a direct example there is Hitoshi's role and reason for being there in the 5th edition Topaz championship. Was he sent because he was the most promising your samurai of a great clan? Definitely not. Now the real reason remains shrouded in mystery even though GMs might have a little bit more clues about it than the players... but not that much.
One of the particularity of L5R is the drama and conflict arising from Honour, Glory, Strife, Ninjo and Giri. Whichever direction you choose, if you can make a plot that highlight these and put each character or the group itself in a kind of dilemma, you will have fun :)