New to metagaming and trying to put team together for Sinnoh Classic

[xVulpes]

Okay so I'm pretty new to the team-building aspects of the metagame and I'm not sure if I completely have it down. I'm trying to put together a team for the Sinnoh Classics competition coming up and I'm still trying to tinker with the lineup I have so far. Being new to this I thought I should reach out and ask for advice especially since I'm really on the fence about which 3 to include and which won't work well on the same team.

Garchomp
-dragon claw
-stone edge
-earthquake
-swords
4 HP/252 Atk/252 Spe
Adamant, Life Orb, Rough Skin
Magnezone
-thunderbolt
-flash cannon
-volt switch
-substitute
4 Def/252 SpA/252 Spe
Modest, Choice Scarf, Magnet Pull
Infernape
-close combat
-thunder punch
-flare blitz
-u-turn
Jolly, Choice Band, Iron Fist
Tangrowth
-giga drain
-knock off
-sleep powder
-HP ice
248 HP/212 Def/48 SpD
Relaxed, Rocky Helmet(or assault vest?), Regenerator
Tentacruel
-toxic spikes
-scald
-rapid spin
-protect
252 HP/4 Def/252 SpD
Calm, Leftovers, Liquid Ooze