Welcome aboard, Matey!
I don't think you can go back to stock SHIII once you have installed GWX. I would play with stock for a while, just to learn handling the boat and shooting torpedoes.
In GWX you get less information on sightings, so it is more difficult to find targets, convoys zig-zab and are harder to intercept. However, the harbours are Alive!
So all in all GWX is more realistic. You may find some useful hints on tactics in my website.
Good hunting, Herr Kaleun
