Is this a game like Silent Storm, where the bullets are rendered as moving physical objects, or is it more like Omerta, where everything is abstract mechanics?

Can you only customize the main character and gather up NPCs to round out your party, ala. Shadowrun for the Genesis, or can you custom build your whole team from scratch?

You only custom build the main character, the rest are hirelings with predetermined builds.
There is a large selection of random hirelings to choose from on each mission.
And a few whom you can befriend or due to other plot reason offer to come with you for free or vastly reduced price (you don't have to take them with you though, you can solo or hire someone else for full price if you want)

Bullets appear as thin streaks across the screen in a fraction of a second to appear fast. I am not familiar with either of your examples though so I can't compare. There is no manual aiming if that is what you are asking, it is turn based and your starts plus random numbers determine if you hit or miss, then after that has been decided the proper animation plays out.

Grenades and fire/mana/lighteningball spells can still hit someone (Friend or ally) if they miss, they just explode at a different random spot

The graphics are a hand drawn 2d background on which 3d rendered people walk. It blends in really well so it looks natural rather then jarring.

The depth is far from Silent Storm. There's no actual physics and the environment is very static. So the depth is more Fallout-like which is not very good considering the heavy emphasis on battles in this one. You can use covers, distance affects accuracy, you can have various skills (Full Burst, Short Burst, Magic...) which add some level of tactics into the game. However, for some odd reason I did enjoy it at least enough to play the game through.h