It's funny how the most famous Nintendo characters are the most difficult ones to analyze for a possible SSB game. And it's because Link's looks are so versatile. Even more contrasting than Mario's alter egos, who share the same big-nosed, moustached face of Mario in them (except when he's a baby, of course).
I believe
Hero of Winds Link can appear in SSBB if they decide to include a
TWW set of characters as well as a set of
TP characters (please, if anyone here has already finished TP and thinks I'm wrong, feel free to correct me).
However, I don't think (now) that the fact that all of those Links look similar (TWW's and
PH's are the same, as you may know) means you should necessarily fuse all of them in one "young" Link especially if you do believe two Links from different games (which is not the case of
Link and
Young Link from SSBM) can coexist in SSBB. What helps you here is the fact that SSB and SSBM state Link's original game as
The Legend of Zelda from NES (probably meaning the version of Link matters little), and
SSBM and
Soul Calibur II use resources from more than only the N64 games.
What would I do if I was Nintendo? Just state their origins as TP and TWW respectively and break their SSB tradition. I'm not sure of what would I do about the names, though. Why "Young Link", if age doesn't matter out of the
OoT storyline? Again, there's something that helps you here, and it's the fact that the character we know as "
Young Link", is called
Child Link in the games, making "Young Link" sort of an universal name.
About the graphics, yes, Cel-shaded style is a good idea for a recent "young" Link. Just keep in mind (unlike some people I've met in other message boards do), that
Cel Shading does not mean "2D"; it means something like "a particular uniform shading in some parts of the graphics so that they look cartoonish".
About the moves, I don't like your
Magical Boomerang much. Magical Boomerang's differences from a regular Boomerang are traditionally its extended length and/or the ability of Link to control its direction once it's thrown. Item gathering can also be done by a regular Boomerang, and would even be a nice easter egg for a regular Boomerang in an SSB game.