what you have currently is an corvette. frigates tend to be a bit larger
btw, you should use the newest drawing of the oto melara gun (it is on the dutch parts sheet and some other places...)
these ships are meant as carrier escorts, right? if so, why not leave the hangar on the carrier and use only an helideck?
for british missile systems: I don't know a lot about those (I know mainly about the US ones, as the dutch use those), but the best would be something like sea sparrow, I guess.
btw, the bow seems somewhat short and the funnel somewhat large. the radar systems are suited for an patrol boat, but you'll need heavier radars if you are going to take missiles on board and give it an frigate role.