Well, dude, you picked a fine piece for what you want it for. For carry, you might want to look at the Milt Sparks VM2 IWB holster. I have three of them now, they work so well. One each for a G27, G29 and a 1006. You'll also need a good GUN BELT that fits the loops on the holster. Milt Sparks makes fine belts, but here the Galco ones and some other will suffice. You want a belt that doesn't fold, a stiff one, or a double thick one that is soft but doesn't fold due to the thickness. The holster and belt are VERY important, almost moreso than the pistol itself. But I gurantee you that you'll be able to hide that pistol well in this rig with some practice. Some guys even hide a G20 and G21 on here, I've seen it.
For ammo, I'd stick with popular factory loads. Stay away from the funky stuff, the questionable reloads, and RBCD for sure. Those loads were the closest I've ever seen to failing in a Glock. For defense, the Winchester Ranger T-Series 165gr. is what I use. I get it for a good price close by. Speer Gold Dot would be another great one. Hornady XTP's in 155gr. ain't bad either. Actually hard to go with a bad factory JHP in .40 in the 155 or 165 grain varieties. The 180's, they may not get the velocity you desire in .40, those are better 10mm bullet weights.
For plinking, any of the FMJ's will work. 155-180. They make 135's, and those may be fine for plinking too, especially blowing up milk jugs. The plated stuff works good too. Just stay away from the lead bullets. Some folks use them in Glocks, but until you feel comfortable doing it, stay away from plain lead, use jacketed bullets. You can read more on this if interested.
I reload, and I load Rainier plated bullets for the .40. I use 180's because I use them in the 10mm too. I load them to the lower end of the data (which is in fact close to the max data too --it has little room for error). It is very finicky to load, and some component makers recommend to NOT load .40 for Glocks at all, so that is why I recommend that you stay with reputable ammo makers.
But yeah, great pistol choice. Oh yeah, remember to keep it mostly stock. A set of Trijicon night sights and a titanium guide rod and a .25 cent trigger job are about all I do (but you don't HAVE to do that, although I would highly recommend the Trijicon sights). You can use the G21 mag release and get an extended one, and there are other slide releases out there. But other than that, I'd refrain from doing other mods to it, especially one meant for carry or defense.
Finally, you should be advised to get a 3rd generation G23, not a 4th generation. They are having problems with their new designs, but the 3rd gens are all great. Problems with 4th gen range from the ambi mag release not working to the recoil system not working right, to the ejector or extractor --it has been everything but an all out recall. Save yourself the headache, get a 3rd gen, you won't be missing anything, trust me. I have six Glocks, early 2nd to late 3rd gen, and all are great. The only problem I had was a ambi mag release G20SF frame I had to return for a regular mag release SF frame --no problems now.
Glocks are notorious for eating anything, but you need to make sure of this with your particular pistol. Fire lots of your carry ammo, get used to it (some on here recommend 200rds. to start) then fire it on ocassion and restock. Your plinking and practice ammo won't be so crucial, just use what works best for you. It does help to use a practice ammo of the same weight as your carry ammo though, but if you carry 165's practicing with 155's is fine too. The 165gr. bullet was designed as the optimum .40 bullet weight by the way.