Marshal Quest:
Silverport only has an "army" in a loose sense of the word. It has several thousand inhabitants with arms, armor, and nontrivial training in the use of these. It does not have a strict unitary command structure for them, as all the Great Houses have their own Marshals.
Your very rough estimate of the forces you have available to draw on at present is as follows:
~500 palace guard, high quality, always available
~1200 soldiers of the Five currently Four Great Houses. Medium quality, situational availability
~1000 soldiers in service to lesser clans. Medium quality, situational availability
~800 mercenaries, thugs, and other hireables on call. Varying quality (the more of them you hire, the more you're scraping dregs), high availability
~600 knightly orders, shrine protectors, cultists, and similar organizations. High quality, low availability.
~1000 trained militia who can hold a spear and form a line reasonably well. Low quality, medium availability.
~Thousands more untrained militia who held a spear for two weeks at band camp. No quality, medium availability.
~200 victims/servants of the Abominations, given various physical enhancements and mutations. High quality, high availability, uncertain side effects.
Under normal circumstances, you would lead the palace guard personally and the clans of the city will lend about half their forces to you. More if the city proper is threatened, less if your use for them seems frivolous or risky. Militia can be called up with public announcements, knightly orders can be asked to contribute, et cetera. The palace guard are the only truly professional soldiers in the city. Everyone else forms up around this strong core under normal circumstances, expected to take your orders, but if you command badly they will start to treat your orders more like suggestions and look to their own officers.
The Portlord has told you that he intends to restore some order and confidence by having you take the army out for a milk run: crushing a barbarian tribe or two in the Bloody Hills in retribution for their raids on nearby trading posts and caravans owned by Silverport. Since such a tribe numbers a few hundred at most and you can easily bring over a thousand soldiers, this should be an easy victory.
You are under absolutely no circumstances to attempt to conquer or even pacify the Bloody Hills, as that has a long history of ending badly after the invading army crushes the fifteenth barbarian tribe and oh look there's barbarian tribes numbers sixteen and seventeen coming out of the woodwork spoiling for a fight. Ride over, show the flag, run up a few easy victories, come home.
Draw up a proposal for at least two thousand troops you want to bring from the above list, preferably up to three thousand if you can. This is intended to form a sort of default baseline for the immediate future. I can't describe all the potentially relevant constraints, but a lot of them should be possible to infer from the descriptions. For example, if you ask the clans to lend you all their 2200 troops for something that's not threatening the city, they will say no. I will answer with available IC knowledge if you have questions about other constraints. You can also write in things like "Hire more mercenaries from abroad" if you think the Portlord and/or Steward will approve.
Here's an example of a possible composition: 300 palace guard, 400 soldiers of the Great Houses, 300 soldiers from the smaller houses, skim 200 decent mercenaries, 1000 trained militia, 400 untrained militia to stand in the back and get battle experience.
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These numbers should not be taken as exact canon for the main quest, as I haven't made sure to check they're internally consistent. But this is what might have come up in Marshal Quest if you'd voted for that.