Can I use wind and solar in the same combiner box? For example, a wind turbine with 3kw and a solar panel with 2kw to be connected together using the combiner box to produce a single output of 5kw.

No, you cannot use wind and solar in the same combiner box. If you program the charge controller for solar, the wind source sharing the same busbar within the combiner box could either cause a serious inefficiency or damage to your equipment. You can, however, use solar power on the bus bar and simply "park" the wind circuit breaker in the combiner box, not sharing the solar busbar or in any way tied to the solar power system within the combiner box.