You will need:
1-2 (33) round Glock mags with some extensions....There are many options in the USA (TTI, Springer Precison, MBX, Taylor Freelance)
2-3 shorter Glock mags for classifiers
2-3 mag pouches
The JP comes with a nice trigger, good Ambi safeties, decent charging handle, etc. You may change those out based on preference but it’s not necessary.