I'm not sure if Volcanion EX is necessary. Ho-oh GX smacks for 180 (210 with Choice Band) which is enough to OHKO most things in the format, especially since many playable high HP GXs are weak to fire. With Sacred Fire being usable after a Phoenix Burn, you can easily get the follow up KO something you didn't quite KO last turn, even if they retreat. With 3 retreat, Volcanion EX is a stall target, and therefore, a liability. Finally, given that your deck space is pretty limited, you don't have the space for energy recovery, which is necessary to keep Volcanion running well. If you run any, I'd only run 1.
I'd bump Ho-oh GX to a 4 count. You REALLY want to start with it.
Turtonator GX is definitely a good play, both for Nitro Tank and as an alternate attacker. Inevitably, Ho-oh GX will go down, and you will need to recover that energy. I might bump that up to a 3-of.
I'd definitely keep the 2 Tapu Lele + 4 Ultra Ball. You desperately want Kiawe on the first turn.
I might drop a Shaymin EX. Scorched Earth should help supplement draw power and Shaymin can clog the bench. (Shaymin EX will likely rotate after Worlds, so it probably won't be legal with the new cards very long.)
Baby Volc is debatable. Usually baby Volc is used to help set up, but Kiawe has you covered there pretty well. I'd maybe keep a couple, just in case you get a bad setup, or you need a non GX attacker late game.
I'd probably only play 2 Kiawe. You most likely don't want to use it more than once, but you don't want it prized either.
(As mentioned earlier, there is a rotation coming up soon. VS Seeker will likely rotate as well. If you want to build for this, just play more supporters or Leles)
I'd dump FFB for Choice Band. The bonus damage from FFB doesn't help you over Choice Band against anything I know of in the format, and with Field Blower in Format, the 40 extra HP isn't guaranteed.
I'm not sure if Altar of the Sunne is necessary. Ho-oh GX is weak to Lightning, and Turtonator is weak to Water. The chances of you running into a Water + Lightning deck is pretty remote at the time. Against a Water deck, just use Ho-oh GX. Against a Lightning Deck, just use Turtonator GX.
Replace Lysandre with Guzma and play more of them. While Ho-oh GX can bench snipe, you will inevitably run into cases where you need to stall or KO something NOW, before it becomes active. You can play around the switch effect, and sometimes it will even be beneficial to have it.
Try to play 2 Field Blowers if you can find space.
Try to make space for Hex Maniac. We're getting a non-GX Alolan Ninetales that has an ability that makes it immune to GXs. Expect it in every Alolan Ninetales deck and some others.
I'd either play more Fire energy or just drop Max Elixir. With 12 energy, on average, you will hit half of your Max Elixirs. You only have 11 right now and, after a Kiawe, you will only have 7 in deck. Couple this with only a 3 count, and you are asking for a dead card.
TL;DR - (though I highly recommend you read through it anyway)
-4 Volcanion EX
-3 Volcanion
+1 Ho-oh GX
+1 Turtonator GX
-1 Shaymin EX (maybe)
+1 Hex Maniac
-1 Lysandre
-1 Kiawe(maybe)
+3 Guzma
+1 Field Blower
+1 Max Elixir
-2 FFB
+2 Choice Band
-2 Altar of the Sunne
+1 Scorched Earth
+1 Switch/Escape Rope(maybe)
+2 Fire(if you can, make more space for more Fire)