What lens should i get
How big are the parts? I mean what's the range of sizes?
How far away does the front of the lens need to be from the guitar parts so that you can light them adequately.-- hide signature --
2X4 inches is the biggest - or a group of 36/72 guitar picks
Working distance on the SEL30M35 is going to be short, but it's the better of the two lenses listed in your original post. The kit lens with a Raynox DCR-150 diopter close-up lens is another option. A longer macro lens such as a manual focus (MF) legacy lens in 90mm-105mm would give you a longer working distance, but you'd have to focus it manually and shoot Aperture Priority (AP).
You may well end up shooting MF AP with the 30mm or kit/diopter lenses. That's how most macro work is done, so using an inexpensive older lens may not change how you're going to end up shooting.
The only advantage to choosing the SEL50F18 is that it can double as a portrait lens, a task at which it excels. You'd still need a DCR-150 or equivalent.