Hmm, this is a rather portentous situation. Renly is dead, and House Tyrell is eviscerated, but King's Landing is in immediate need of rebuilding. However, Stannis can't immediately move to address the massive refugee crisis until the last vestige of a threat to his rule is shattered. The Golden Company and their claimants have to be the first priority.
If I were a betting man, I place a rather large wager on one of two scenarios occurring within the Targaryen camp. One, they immediately relocate to Harrenhal and prepare for a siege as best they can. If they think they can prove a tough enough nut to crack, the chances are they'll try to sue for peace and a safe passage back to Essos in exchange for handing over "Aegon" and Daenerys. When it comes down to it, the Golden Company and whatever other forces the Targs might have are mercenaries, coin and glory are only worth anything if you're not dead. The other scenario, is that Aegon has them fall back to Crackclaw Point, and begin reinforcing his army with Clawmen loyalists. Of the two, I'd much prefer Harrenhal to a long running guerrilla insurgency.
Also something that must be kept in mind is the Dornish host we got word of, that was marching north to link up with the Targaryens. In regards to this, I'd suggest having Randyll Tarly, in his new position as Warden of the South and Lord Paramount of the Reach, take an army down south to meet Oberyn and his troops. Have Beric Dondarrion go with him, along with a good number of Stormland levies.
Next I would split the remainder of Stannis's host into two parts, one to keep order and begin rebuilding at King's Landing, and the other to march east and deal with the Golden Company. I'd take half of the Riverland forces and most, if not all of the Vale army, which should give us between 50,000 to 60,000 men. A more than comfortable margin of numerical superiority when dealing with the Golden Company and whatever mercenary supplements they have.
In regards to the Reach...there really isn't any time to deal with the minutiae right now. That said, there are a number of things we should address. House Tyrell of Highgarden is to be unlanded, with Margaery to be married off to Dickon Tarly. Garlan is to either take the Black, or face execution. Willas can do the same, but with the Maesters or Sept instead. House Tyrell of Horn Hill is to be treated the same, one and all, and stripped of all titles and lands. Any loyalists of Renly's are to be beggared as well, and any captives can either be ransomed for a fortune, take the Black, or be executed.
This talk of demanding that levies are to be gifted to the Wall....what the fuck are you smoking? You can't order levies to the Wall. It's an individual choice that can't be "forced". The fuck is this insanity. Those men are needed back in the Reach to harvest crops, which we will need to feed what is now a quarter of a million homeless subjects.
Also, Jaime is now thrice over an oathbreaker, a cuckolder, and a kingslayer. No, I'm sorry, but once he recovers he will be given one of two choices. He can serve out the rest of his life as a Sworn Brother of the Night's Watch, and maybe regain some measure of honor in time, or he can march to the headman's axe. Kevan can be released to return to Casterly Rock, and Tywin will remain as a hostage.
Taking all of this into account, I offer this plan:
[x] Plan: War, What Is It Good For
[] In light of his injuries, Jaime Lannister will be kept in Stannis's custody until he recovers under the treatment of a maester, after which, he will be given a choice. To serve out the rest of his life as a Sworn Brother of the Night's Watch, where he might one day regain a semblance of honor, or to march forward and be greeted with the headman's axe as justice for his many, many crimes.
[] Randyll Tarly is to be raised up as Lord Paramount of the Mander, Lord of Highgarden, and Warden of the South. In standing with his new duties, he will march south to meet the Dornish host with an army made of both Reachmen and Stormlanders. Beric Dondarrion shall go with him. Ravens are to be sent out that any lord wishing to profess loyalty in the Stormlands and Reach shall join a part of their levy to his host.
[] Garth Hightower is to be given leave to besiege and sack any Reachlords that do not bow, whose lands shall then be divided up amongst royalist second sons and claimants. House Tyrell is to be stripped of all their lands and titles. The men of House Tyrell shall either take the Black, join the Citadel, swear to the Sept, or they shall soon meet the Stranger themselves. Margaery is to be married to Dickon Tarly to cement Randyll's rule.
-[] Lords that did not strike their banners for Renly shall be heavily punished, but that is to be done at a later date, when Stannis isn't fighting a war on two fronts and King's Landing is more than just a smoking husk.
[] A mixed host of loyal Crownlanders and Rivermen is to remain at the ruins of King's Landing, under the command of Davos Seaworth, to begin efforts to rebuild and to maintain order. The remaining host, mainly consisting of Valemen, is to march east with Stannis to confront and deal with this Targaryen pretender once and for all.
-[] The Blackfish is to be given command of a group of outriders and scouts to gain as much information as possible on the Targaryen pretender forces.
[] The sell sword Bronn is to be knighted and given the hand of Brienne of Tarth for slaying Loras Tyrell in open combat. (If this is accepted. I just like the idea of Loras doing a bunch of fancy sword twirling and then Bronn just shivs him when he's over extended.)