There is an indepth view of the Hyuga class in Seaforth World Naval Review 2014
One thing that struck me was that they have significant capability other than just carrying helicopters - with 16 surface to surface missiles, 12 ASROC, 6 torpedo tubes and 2 Phalanx as well as a locally developed multi-function radar system that looks like a Junior Aegis.
The Izumas look generally similar to the Cavour - so a small air group of F-35's is quite possible
Also interesting that thee japanese navy has similar manning issues as the RN