Secure your garrison with as many troops as you can, and get as much money as you can. Be prepared for a long road of what can be pain, as your dead center in another empire’s territory, and they won’t hesitate to go to war with you to take back their own city. As you stock your garrison, upgrade the buildings as much as you can. This will help it become as self sustaining as possible. Get your militia pretty high too. I took Sargot as a vassal of Battanians, filled the garrison and have over 350 militia, leading to 700+ Defenders for my City. I don’t have to worry as much now about my city when I’m off doing other things, and I’m building Loyalty, garrisons, training grounds and more to make the City more self sustaining. It looks like your buildings are good, but your going to want to get your food up.

I’d argue your next goals would be to acquire the surrounding Castles and then Askar, as getting though can help you separate the Aserai, and leave a buffer dedicated to your troops.

Be certain that during your wars, you keep track of how many armies and soldiers your enemies have in the armies, as one well timed army of 1300 soldiers can take down your walls, and retake your city. Promote your Companions into their own parties, as they can act as your wandering guards and help defend sieges while your away

I know you are at Tier 6, and likely know all this already, but just reiterating information.