My bad on the bridge, forgot to check the window size, it's fine as it just looks too plain with no details of any kind on there right now, pretty much all Starfleet bridges have a dome above them (so the Captain can enjoy a real view of the outside?) and various greebly type things around the dome just to add detail really. I completely agree with the registry change, make sure you keep the '8' at the front as there are too many 7xxxx registries everything from before TNG to after Voyager has regs in that range, the only higher number so far has been the Norway (USS Budapest weighs in at a hefty NCC-84923).
The torpedo launchers, I'd stick with 2 one on each side as this is the arrangement the lowly Nova science ship has in canon; given the more combat oriented mission profile of this ship I'd even suggest adding a third launcher to the rear arc. Regarding designations, the Defiant was an escort, I think that implies the role of such ships in Starfleet's 'Politically Correct Naming Scheme'.