Well, the T-250 is technically a longarm with all the benefits and drawbacks which come from that. So, BF is out of the question as uncompensated recoil causes double penalties. Besides that, it would empty out the magazine in basically one go.
Standard choice for me would be to saw off the stock via the Sling mod. Now you've got a pistol-grip sawed off. Doing a barrel reduction for an additional -1 to the conceal drops its range by 80%, which is only a few meters at this point, and makes the minimum choke medium spread. Might not be a bad idea if you're really worried about keeping it hidden and don't really plan on using scatter-shot (80% of taser ranges? yikes.)
So far, you've spent 30¥ and have a 5mag shotty with -1(0) concealability. Weapon's still legal at this point.
A barrel-mounted silencer, while more conspicuous and not as effective as an internal one can let the gun be both legal and illegal as needed, but, since you're looking to maximize damage potential, you'll be using illegal loads anyway. Might as well drop the silencer into the barrel for that good -6 to hear. Throw on a personalized grip so you don't have to keep the sling on, and you're quick drawing a shotgun. Awesome. Then it's all about that standard Explosive load. Half the price of Ex-ex, with the only difference being the lack of -1AP, which is a pale cousin to the +1DV.
Really though, autofire is the only reliable way to increase a weapons DV output, and a small shotty isn't built for burst. Modding for BF would take up 4 slots. Adding an Additional Clip for a decent magazine capacity would take the remaining two slots and up the concealability by +2.
If maximizing concealability isn't an issue, then the Additional Clip mod could be a good choice for the first build with the silencer. Just do an external smartgun link or laser sight, and you've got the room for modding it. Now you've got a shotgun with +1 concealability that can have two different 5m loadouts, so you can have a pipe full of standard loads and a pipe full of wacky loads.
Also, because it came up earlier,
here's some hip-hop unlike any you've ever heard. Youtube's crappy compression can't handle it, though. It's too heavy.
Or, on the completely opposite side of the spectrum
there's this.
Music is rad.