Welcome to the forum!
The best thing you can do right now is, shoot it! No upgrades necessary. save your money and buy ammo. Learn to operate the gun and get familar with what you like and dislike about the cal. and gun. I would strongly suggest you shoot about a thousand rounds, one hundred at a time per range time. Learn to clean and oil it as per the OME manual.
Sound advice. You can never go wrong with correct practice.
Tricking a gun out usually reduces it's resale value and in many cases never improves the ability of the gun.
True, BUT Tricking out a gun is a matter of personal preference and "making something your own". It may hurt trade in value, but it May or may not affect a private sale. It's like adding stuff to a motorcycle or a car, the dealer isn't going to give you any extra b/e you have a super exhaust or nice wheels when you trade it in. But some people like to tinker. If it helps you learn your weapon better, so be it.
It just seems strange to me so many people buy a GLOCK and then want to change things when most often, it is the first gun they have ever owned.
As far as I have experienced (this is by no means an "Absolute" statement), People get conversion kits to shoot other calibers mainly for the savings in the cost of ammo. Unless you're going from .40 to .357 SIG. Then it's to save on not having to buy another gun. I say, to each his own. You can have multiple caliber for the price of a barrel and some mags. Pretty good to me.
As with all things, YMMV.
D