Black Maester Sam

Yes, Tarly does seem the type for that, given what we know from Sam about his upbringing and how he ended up at the wall. But I can see this scenario only playing out, if Dorne doesn't declare for Aegon and tries to wait for Daenerys, otherwise there won't be enough people left to oppose Aegon for a while an his arc becomes boring. There was a quote, I think from Tywin, that every great lord has unruly bannerman. Lannisters had the Tarbecks and the Reyns, Starks have the Boltens, Tullys have the Freys (and/or Darrys). I can't remember if there was also one for Dorne. I dont think the Vale or the Reach was mentioned though.

Mace Tyrell is in charge of the Small Council for now and he hates the Dornish, especially the Red Viper. He won't be happy to learn, that his bastard daughter has a seat in the council and Kevan didn't tell him. He is more likely to insult her or deny her the seat, than to listen to her, thus driving Dorne into an alliance with Aegon. I think there will be war in the Reach/Stormlands/Dorne between those that accept Aegons claim (Dorne and some or most Stormlords) and those that think he's fake Aegon (the Tyrells and most Lords in the Reach). This war will devastate large regions of the south and deplete there armies.

I never said the Tyrells will win the Battle. In fact i think that Connington will win, because Mace is overconfident and will make mistakes.

The Golden Company captured Storms End and the Tyrell host is in KL. When they fight, it will most likely be somewhere in between. The GC has 10.000 men at full strength, but we know they need some part of that, at least for now, to protect their positions in the Stormlands. So far as we know they don't have any military support or alliance in Westeros yet. They have more experience and better discipline, and the elephants could be a strategic advantage. But it's cold enough to snow in KL in the epilouge chapter and some time will go by before the 2 armies meet. I'm just questioning how much of an advantage elephants are in a fight under these circumstances. I'm not sure how many men the Tyrells currently have in KL, some portion is still on Dragonstone, a large part was sent back to the Reach to deal with the Ironborn and they won't leave KL unprotected, but they can probably send 20.000 - 30.000 men against the GC. This should give them the advantage over the GC for now. But we also know they don't really seem to regard Connington and the GC as a big thread to them, from what Kevan has seen in his last Council meeting, so they might send a smaller portion of their host against Storms End. I do think the GC has good chances to win the first battle against the Tyrells. When Connington manages to forge an alliance with Dorne and/or get support from other Lords in the south after that, then he can turn the tide in Aegons favor. Especially since Varys will continue to sabotage the Lanister/Tyrell alliance from within KL.

They have only found 3 elephants for now and it's winter in westeros. This may not be the best climate for elephants to be useful.