Knowing the scale and flight style now makes this easy. For that size of model a 1/4 inch sq ended trailing edge on the wing or tail if fine. The tail won't really noice that much and on a wing that thick a 1/4 inch trailing edge is not really sharp but hardly blunt either. It'll be fine.

However, I'm thinking here that 1/4 inch thick tail surfaces on a model that size is very thin from a structural standpoint if you expect them to not twist and possibly flutter in that much of a propblast and given the size of them. I would suggest you go for 1/2 inch thick for the main part and then taper the elevator and rudder down to 1/8 to 1/4 at the trailing edge. That much thickness would provide a far more sensible amount of surface stiffness for this size of model.

And remember. Rounded edges for the leading edge and tips but leave the trailing edges squared off so the air flows off easier. Rounded trailing edges can lead to flutter easier than squared ones. Properly tapered edges also are more flutter resistant but how much you want to put into this is up to you.