Glad you're enjoying the bass
That buzz will go away after a few sessions of playing, though I personally love a nice crisp new string and the twang I can get from them, especially when slapping. I would say stick with roundwound because you already have a "P" type with flats, the JB should be nice and crisp and burpy with some rounds on it. And yes over time you will learn how to approach the strings to either achieve or eliminate the buzz; though it sounds pretty self explanatory, the more parallel you can keep your finger strokes or pick strokes to the fretboard, the less buzz you're likely to get, however the more perpendicular to the fret-board your strokes are the more likely you are to get buzz..... also if you're getting uncontrollable buzz at any one particular fret you might need to have the bass setup and the action raised slightly
