Watch what you paint it with. The higher nitro fuels need proper butyrate dope or something exotic. And if you're using one of the exotics then they get heavy really fast.

I'm assuming that it's the 32 inch span Hellcat. There's still not a lot of wingarea on that puppy so watch your weight buildup carefully. I sure would not want to see the ready to fly weight get over about 18 oz tops or you'll find it's a snap rolling monster at the worst possible times. Add up the weights of all the radio components and engine plus fuel tank and any other fixed overhead weights. Subtract that from 18 and you'll have a target weight for the total airframe and covering. Tissue and dope will add about 1.5 oz roughly so deduct that as well.

Silkspan will certainly work for you but japanese tissue or even light art store tissue will work fine as well. On this size of model you're just trying to use the paper to act as a grain filler over the sheeting

If you're planning on adding a better spar plus sheeting to the wing I'd suggest you just scrap all the wing parts and go with a better airfoil than the simple flat bottomed one. Using a new airfoil will make it a lot easier and lighter to make the wing in the end.