I've just had flashbacks to welding my moggy up. I did the wheelarches with flat plate and chopped it and beat it and it looks fine as I wasn't after a concours car. The main thing with welding is to keep plodding on and before you know it, it will start to take shape.
Regarding how you finish your welding off in the wheelarch, there are flapwheels available for 4 or 4.5inch grinders that allow you to almost polish the weld down to where you want without leaving grinding marks its a must have tool much less aggressive for cleaning metal up aswell.
Phil<br>