Before I say anything, your team is rather slow and Gothitelle can use that Trick Room TM. I think it would really benefit your team.
Torterra seems pretty good. Do keep in mind that you've got some breeding options. Body Slam's 30% paralysis chance can support your team as well as help with Torterra's speed. Synthesis can restore the health you would lose while buffing. You can also breed Swords Dance onto it. Have a Smeargle/Zangoose breed Swords Dance onto Rhyhorn/Rhydon, then breed that onto Torterra.
Note that you can get both Body Slam and Swords Dance in E13, both parents will be able to pass on moves then. Have Tropius breed Body Slam onto Turtwig, have Smeargle/Zangoose breed SD onto Rhyhorn, then breed a male Rhyhorn with SD and a female Turtwig with BS to get the egg of a Turtwig with BD and SD.
Gothitelle can get Energy Ball. Breed a Lotad with Cacnea, then Cacnea with Gothitelle. Cacnea also learns Dark Pulse by TM, which you can then pass onto Gothitelle as well. Dark Pulse has the same power and coverage as Shadow Ball, but it's secondary effect is better and more likely to occur.
With your team Trick Room would work really well. A set of Dark Pulse, Psychic/Psyshock, Energy Ball, Trick Room would be ideal.
Hitmonchan is in the game. Trade a Dunsparce to the guy on the roof of the building in the top left corner of Route 1. By level-up, it learns the 3 Elemental Punches, Bullet Punch (not necessary with Trick Room) and Close Combat. Machamp can also have the ability No Guard. With it, Dynamic Punch is a 100% accurate, 100 base power move with a guarantee to confuse foes.
Discharge has a 30% paralysis chance, and that should be enough already. Dragon Pulse could really help you out thogh, seeing as we might soon be fighting the Dragon Leader. Cotton Guard could aslo be fun to play around with. If you want to roll with Trick Room, you can breed Thunderbolt onto it via Pikachu. Not paralyzing (reducing the speed) of foes would be great with Trick Room.
Pretty good Granbull. No comment on that one.
Not really, sorry. Slugma does not learn Energy Ball via TM, so it cannot learn it through breeding. I also think Cottonee isn't around since E10. I think. You can still use Swirlix though. You have two options for it:
Have Castform learn Energy Ball through breeding with Swirlix/Slurrpuff and Fire Blast through level-up and pass that onto Chandelure
or
Wait for E13. Then, both parents will be able to pass on moves. Have Slugma/Magcargo pass Flamethrower to Litwick, Have Swirlix/Slurpuff pass EB to Castform then breed that female Litwick with Flamethrower and male Castform with EB and get a Litwick with both.