If you want a CL then build/buy a CL. If you want a DL then build/buy a DL. Don't mix the two together and try some cut-price deal. It doesn't work.
A DL is never a true CL and a CL would be wasted herding a flock of DD's around and could get hurt in the process. Why not just eke out the time and money and get a couple of German CL and build a couple of a super-DD type? That way you get ships that are best for the roles they are designed for rather than using ships for the wrong things.
Don't over-estimate airpower, they have to find you ships and then score hits. You have land-based fighters too for air support so things aren't too bad.