I have recently taken out an existing hardwood floor to repair some structure.
I have an older house with 2x6 joists on 24" centers. On the joists are 1x8 ship lap style decking, except for the area that I repaired which is now 3/4" plywood.

What should I put down on top of the decking and plywood before putting down 3/4" hickory hardwood? My thought was 3/4" OSB, but some people are telling me thats overkill. should I go with 1/2" or 5/8" instead? Height is not an issue. Also, better to use OSB or Plywood? Also, since the ship lap is not really well sealed, should I put tar paper on top of that to help with moisture control? I am going to put aquabar under the final hardwood flooring.

Sorry for all the questions.

Thanks

Sonny