Personally I'd go with a small amount of cruiser turrets, MAYBE 1 gunboat missile as a fighter screen, to make it a carrier escort ship.. though honestly it's quite a hard area to delve into.
it would have a low core, focus mainly on primaries, razors and pulses as opposed to mortars and cruise missiles.
The ship itself would have to be big, something along the lines of a Bretonian gunboat (which is likely the best candidate for the class), very bulky and easy to hit with caps/bombers/everything, but not long like a cruiser.
it would be effective in small groups, repulsing destroyers that attack carriers, totally useless on its own due to low defences and agility, any destroyer can mortar a bret gunboat easily.
For turret numbers, liberty/bd cruiser have the lowest amount as destroyers, but a powerful forward gun, the bretonian gunboat has a forward gun too (a very big one), but 7 would make it practically a cruiser in firepower sans the powercore, it would end up with 4, 5, maybe with maybe one gunboat turret, with a more powerful forward gun, 5 would probably be good.
Its defences would be barely changed, more armour and botts, 100 or so botts and 40k or so armour just as a prod in the dark. Agility would be slightly more than a light cruiser, more mass, between gb and cruiser (that's strafe for normal people).
I'll say here though, it'll likely totally suck, or be quite powerful, the gunboat turret/s is a big issue, though I personally dont expect a -single- turret will result in much more spam than normal (a normal heavy 600k gunboat can spam a basic missile veryyy nicely), reduced agility might hit effectiveness too.
Despite my ideas here, I cant say if I support it or not.