i had this massive wall of text but then i accidentally changed webpages :/. so here the short version:
guide to competitive tf2 clan matches :
http://www.gotfrag.com/tf2/story/43759/indepth guide of eahc class, settings:
http://www.ubercharged.net/how-to-play-tf2/the-competitive-tf2-guide/basically tf2 clan matches are played in 6v6 with 2 scouts, 2 soldiers 1 demo and 1 medic. 2fort is not played and Koth_viaduct is the only koth map played. cp_badlands, cp_granary, ctf_turbine, cp_yukon, cp_follower and cp_gravelpit are played. you find more about rules and such in the guides. to find 2 more clan members, go to gotfrag.com and their tf2 section. WARNING: the gotfrag section of tf2 is not monitered and a lot of trolling is done. your recruiting post may look like ppl are rediculing you, but don't take that seriously.
2 more things. first, I understand that you ony; have 4 players. you'll have a hard time finding a clan consisting of only 4 players or a clan that will play you at 4v4. also, whatever classes played (again, 2 scouts, 2 sollys, 1 demo and 1 med 80% of the time) will use the default weapons. the soldier/demo weapons are banned form leagues until firther testing/tweaks are done. for snipers you drop a scout for sniper usually, and sometimes soldier, but either way the reliability of a hitscan weapon of the sniper rifle trumps the projectile (and therefore the ability to dodge) of the huntsmen.
scout: Fan is acceptable to use however frowned upon using because the mechanics are broken
Bonk: used really only at the beginning of gravelpit to try to get the demo to blow his sticky trap, used by blue team and always paried with the scatter gun.
Sandman: banned from play because the mechanics break the game.
soldier/demo weapons under testing
pyro: flamer over BB, reflect is 10x better then the crits. shotgun over flare, axetinguisher (falre is used sometimes though)
heavy: sasha, shotty, KGB (sandvich used rarely thanks to new throwing mechanic)
medic: needlegun (gives better HP regen than blutsauger), and uber saw are used. kritzkrieg is the best (and most used) unlock in TF2, used alot by medics.
sniper: rifle (sometimes huntsmen), smg/jarate (your choice)
spy: revolver/ambass (again your choice), and any of the watches.
i hope this helps. any questions? post in this thread and I or any of the other 6v6 players will help. tf2f also has nightly pugs (6v6 pick-up games) at 11:30 EST, and it's a great place to try out 6v6.