With Riften and Windhelm under sieged, I will send in a smaller force to watch out for reinforcements from Dawnstar. Winterhold won't be much of a problem so I will ignore that. Once I taken Windhelm I will execute Ulfric, And send most of the troops in the siege to reinforce Riften attack, attack Dawnstar, and attack Winter hold, both of the latter should be easy due to weak defenses. And the rest will occupy Windhelm, which would be my HQ.
Whether I took control of Eastern Skyrim by Diplomacy or through conquest I will send a diplomat to Solitude To tell Tullius that we are not a threat and will give back eastern Skyrim after Akavir has a strong presence in Tamriel. That way I can wait for reinforcements from Akavir bringing both Soldiers, and Colonists. And have more time to prepare an attack on Western Skyrim. Ofcourse I will legalize Talos worship to get support from the Nords.
When I am ready I will use Dawnstar as point where my navy will attack East Empire company's ships like pirates, and even the ports of solitude, to weaken trade between Solitude and High Rock weakening Skyrim's economy. My forces will launch an attack on Whiterun. When I take the hold I will still keep Balgruuf as Jarl as long as he is loyal to Akavir and support the war. With the trading hub of the province under my control I can practically have a grip to launch an attack.
One by one I will take over the westen holds. When I take Morthal, which should be easy, I will then launch a siege on Solitude. I will make another blockade and send in an army to split the city from the rest of the hold. Ofcourse I will send in a smaller but still large army south to prevent reinforcments from Cyrodill. Ofcourse if I have the stormcloaks on my side the bulk of them will be there as well to assist the flank. After a few weeks attacking the city I will personally lead the assault to the city. After taking it I will keep the current jarl and make her a tool for my country. Of course, Solitude will be my new Head quarters.
With the only two holds belonging to the empire; I will send in about 1/3 of my men to Falkreath and Markath to invade it. The rest will occupy the rest of Skyrim and Morrowind. If I have the stormcoaks support most of the men attacking the reach will be stormcloaks led by an akaviri general with Akaviri support. Falkreath will be an almost enitrely of Akaviri. Falkreath, because of a weak jarl, should be easy to fall. I will split my Falkreath army into two. One guarding the Skyrim/Cyrodil border, the other assisting the invasion of the reach. Now the reach would be my hardest fight yet. The defenders could easily destroy bridges, forcing me to travel through the hills, and abandon most siege equipment, and don't forget the Forsworn. Now if I somehow took the reach I will have a joint Stormcloak/ Akaviri (Or just Akaviri if I had to invade east skyrim.) occupation of the reach suppressing the Forsworn.
Now I will again set up defenses in Syrim, encourage more colonists, and await for more men. During the mean time I will send in a diplomat to convince as much as the High Rock Kingdoms as possible to side with me. After with Cyrodil cut off they can't ask for help when we attack. If there are some that still refuse they will eventually become conquered. I will send in two armies. One to Daggerfall, (reinforcing the ones who side with me or attack depending on what Daggerfall chosses.) And the other to Northeastern High Rock. (Same reason plus to have a better security around Solitude.) And just eliminate the kingdoms that sided against me. When I am done I will set up an Akaviri to become Governor of The akaviri province of High Rock.
Now I will try to get Hammerfell and the Aldmeri Dominion to side with me. Problem is I see Hammerfell refusing to do so because the thalmor are allies. If that's the case then I will leave Hammerfell alone.. For now. With the two or three of us we invade Cyrodill. I will attack from Skyrim and Morrowind, THe AD will attack from Valenwood, and HF (If they do join.) Will attack from... Hammerfell. Phase one will be me taking The Valus and Jerral mountains, The AD taking the Golg Coast, And HF (again if they do.) taking the Colovian Highlands. Now we will adavance through Cyrodill eventually taking the Imperial city.
Once the empire has fallen there will be a treaty about who owns what part of Cyrrodil. I will The Jerral and valen mountains, The Nibenay Valley, Great Forrest, and eastern blackwood. The Ad gets southern Colovia and western blackwood. Hammerfell would get Northern Colovial. (If they don't it will be mine.)
Now after all the fighting I will then report to my superiors that I completed my mission.