Welcome from Idaho Sugarpit! I don't own a glock but there are plenty of glock owners on here... Under Forums scroll down to Glock and read away! If there aren't any similar threads, try posting your questions there...
On the subject of your upcoming Glock purchase: I think it's a good choice. Only shoot ammunition with jacketed bullets in it (no bare-lead-bullet reloads), and stay away from cheap "gunshow grade" reloaded ammo. It's a high-quality pistol, so feed it decent ammo for best results. I'd recommend Blazer or Blazer Brass, Remington/UMC, Winchester white box or white box bulk-packs, Federal American Eagle, and/or any high-quality defensive ammo with JHP bullets.
Welcome to the forum. Excellent choice in a firearm. The G21 is a full size duty pistol so you will be very aware of its size as you begin your journey of concealed carry. I currently carry a full-size semiauto and like the assurance of maximum available firepower should the need arise.
As a matter of opinion, try to purchase a model 21SF (Slim Frame) which came to market a couple of years ago and is now widely available new. The grip area of the gun is much easier to grip well and will save you some frustration. Glock has a long way to go with all things ergonomic but they make a completely reliable handgun.