I think its a good idea, but I would increase the ammo for one as if its a PD system it needs to shoot out a large quantity to (hopefully) hit a missile, and I would increase the OP to 10 as it seems like a military weapon so not widely available for commercial use.
I actually disagree with the latter notion! Private superyachts in the real world do mount anti-missile countermeasures (e.g., the Eclipse). The details are sketchy, since seems to suggest more that it's just radar and ECM, but it's not a huge leap to imagine flares, interceptor missiles, and the like in a sci-fi universe.
Since the Starfarerverse is post-Collapse, legal restrictions pretty much go out the window in favour of not 'taking the sky' from anyone, too, and if anything needs defence against missiles in the Corvus system it's a big hulking freighter or an otherwise-unarmed luxury yacht.