Soldering the ground to the tone pot is fine. But it looks like it's a cold solder joint, meaning that you didn't get the back of the pot hot enough to make the solder flow onto it...it's just blumped up on it. This may lead to a poor electrical connection. You should let your iron heat up then touch it to the back of the pot and the side of the solder blump again (don't put the iron in the solder blump). If your iron is hot/powerful enough, it should cause the solder to melt and flow onto the pot. If your iron is less than 40 watts you'll have a hard time doing this without damaging the pot (you've got a lot of solder there to heat up).
As far as a neck pup, I agree that you can't get much better than the Jazz (I personally prefer the Jazz bridge model in the neck).
As far as a neck pup, I agree that you can't get much better than the Jazz (I personally prefer the Jazz bridge model in the neck).