First off, if you're planning a Fire monotype team, I'd strongly suggest bringing Torkoal along. Stealth Rock is going to be your team's bane - especially for Talonflame and Charizard - and Torkoal is the only Fire type who can learn anything that removes hazards. You should also make sure none of your pokemon has even HP once EVs are calculated in; because Stealth Rock damage is based on a fraction, having odd max HP could mean the difference between being able to switch in once or twice. Now, on an individual level...
Mega Char Y looks about where he should be. His stats make him a great special sweeper, and the combination of moves you've given him work for that. Focus Blast is an option in place of Dragon Pulse; it hits more pokemon for SE damage and has more power, but it's notorious for its inaccuracy.
For Rotom, I think Volt Switch would be your best bet for the third slot. Fourth can be Pain Split (which will more often than not heal Rotom thanks to its relatively low HP) or Dark Pulse (for added coverage). If you want to switch his item out for a Choice Scarf or Specs, you could also put Thunderbolt or Trick in this slot.
Heatran is something I more often see as a tank rather than a bulky attacker. Personally I'd switch out one of its attacks for Roar, Taunt, or Toxic.
Volcarona works, but I don't see a lot of point to ChestoRest when it has access to Roost. I'd say if you go for Fiery Dance, no point in Quiver Dance, or vice versa. You could also potentially run Giga Drain, since Grass takes out every Fire weakness. Whatever the case, I'd strongly suggest going with Swarm and have him hold a Life Orb, since that'll give you stronger Bug Buzzes once your health runs low.
For Talonflame, that's pretty much the standard, with U-Turn being used for the last slot. If you're going to stick with Choice Band, replace Roost with Return, but otherwise, swap the item out to Life Orb. Choice Band cannot be used with Roost effectively.
Infernape actually fills a nearly identical role to Talonflame, only with slightly different coverage. He does have Sludge Bomb as an answer to Azumarill and Sylveon, which will be stronger than Thunder Punch, but have less accuracy and less coverage. Also I'd say go Flare Blitz over Fire Punch unless you don't want the recoil.
A couple other options you may want to consider:
Torkoal @ Leftovers
Clear Body
Bold
252 HP, 252 Def, 4 SpDef
- Lava Plume
- Rapid Spin
- Clear Smog
- Stealth Rock/Yawn
Both built to tank and act as utility. Lava Plume for STAB and for its 30% Burn chance, Rapid Spin to wipe away the dreaded Stealth Rocks, Clear Smog to neutralize setups, and the last move either for Stealth Rock or Yawn. The former is less necessary since you've already got Heatran, but Yawn has its place since you don't have a Sleep inducer in the team.
Emboar @ Assault Vest/Choice Specs
Blaze
Modest
252 HP/Def, 252 SpAtt, 4 SpDef
- Fire Blast
- Scald
- Focus Blast
- Grass Knot/Solar Beam
Emboar has some great bulk in the form of its high HP, which IMO makes it a great Assault Vest user, but he's also useful as just pure bulky offense, which allows you to use Specs well too. Fire and Focus Blast are for STAB, Scald and Grass Knot/Solar Beam for coverage. You'll need to watch out for the Dragon/Flying types, as well as Lati@s and Dragalge, but this guy is one of the few that can take on Fire/Flying types well.
Delphox @ Power Herb/Fire Gem
Magician
Modest/Timid
252 HP, 252 SpAtt, 4 Speed
- Psyshock
- Magical Fire/Flamethrower
- Wish
- Solar Beam
Only two Fire types can Wish, but Wishing can be fairly useful for you bulkier pokemon, and of the two Delphox has the higher amount of HP. However, its primary focus is in offenses; Wishing is just its fun little utility thing.
Darmanitan @ Life Orb
Sheer Force
Adamant/Jolly
252 Att, 4 SpDef, 252 Speed
- Flare Blitz
- Rock Slide
- Zen Headbutt
- U-Turn/Belly Drum/Bulk Up
One thing your team lacks is a really good stop to Talonflame and Mega Char Y, and this works as one thanks to Sheer Force Rock Slide. The Life Orb is probably your best bet for an item since its recoil is prevented by Sheer Force. I included U-Turn as an option last slot, but you can try Belly Drum if you happen to be willing to risk it, or Bulk Up to set up a bit more.
