score:9
Brandenburg Gate will be horribly crowded, but so will be all clubs. If you come from Schönefeld Airport (I assume that is what you meant, IATA code is actually SXF) it might make more sense to store your luggage at Südkreuz Station (which has a direct connection to Schönefeld) because from there you can switch trains (from S45 to S2) to go to Brandenburg Gate (although this will be really, really crowded). Details for luggage storage at Südkreuz are e.g. here. If you are up for a walk or rent some bicycles there is a cycle track along the Metro line from Südkreuz to Potsdamer Platz that should take thirty Minutes at max (and from there you are pretty close to Brandenburger Tor). Scenery is nice, but at New Years eve you might not be very interested in sightseeing.
Judging by the lineup for the last New Year's party ("DJ BoBo, Jermaine Jackson, Marianne Rosenberg, Rainhard Fendrich, Max Giesinger, Bonnie Tyler, Peter Schilling, Fun Factory, La Bouche, Kerstin Ott, Wincent Weiss, Venga Boys, Ray Wilson, Radio Future und die Hermes House Band ") you actually might want to avoid Brandenburger Tor if you insist on Techno, but if you are simply looking for a huge party then you should be fine (alas at 46 I don't think I can recommend anything that would be much fun for a group of 19 year olds).
You can look at https://www.berliner-silvester.de/ to get updates on the planned festivities (I also recommend to read the bit about security checks).