I'd buy at least 2. I have 20 FBMG mags, but have 50 G3 mags just sitting and waiting. I bought them just because they're cheap right now, same with FAL mags.
Have you put the trigger guard on yet? If you have and the nut/screw head is too large or off center the back of the legs for the trigger will hang on it and keep it up so that the hammer is captured.