You won't need to alter the wing chord. Remember that the two wing areas add up.

The bigger issues will be how to install the ailerons in the cardboard wings. For this I'd say just add strip ailerons to the bottom wing and call it good.

A .40 should fly the model just fine. Or a GOOD 4 stroke .45 to .50. By the time you modify the model for RC you'll likely add about a pound to the weight. But a 6 lb Jenny biplane will still have a decent wing loading. But depending on the airfoil it has there may or may not be some bad charactarisitics. If it didn't have a harsh stall during the glide in landing approches as a CL model then you should be OK as an RC model.

The elevator hinge is going to be fine regardless of where it is located. If it's at the scale location then you won't need a lot of surface deflection. Likely a 1/2 inch each way will be plenty. Same with the rudder assuming you use the scale hinge line location.