If you are going to carry, you need to dress around the best weapon for you. Not get a gun that fits your current style of dress. If you want a gun that will save your life, you should get the best gun you can get. If you are not willing to adapt to the best tool you can get, you are not really ready.
I can carry a compact pistol (Glock 19/23, HK P2000) In a IWB holster all day long with no issue. I've taken naps on the couch with them on.
For pocket carry, I have a Taurus .38 that I carry in a Desantis Nemesis pocket holster.
I can carry either or both in slacks, button up shirt and a tie.
While true, I still disagree. The clothing you wear should be included in the best gun for you. If I live in a cold climate where layers of clothing are normal, then I could carry my full sized P99 without issue. In a hot climate where I need shorts and a tshirt, I'm not going to conceal that thing (would look like a huge growth under my shirt). Thus I would need to pick a smaller firearm.
I carry a walther PPS. It's small 9mm and holds 7 rounds. I can conceal it with nothing more then a IWB holster and a tshirt. It's also light, doesn't require a huge belt and doesn't hurt to sit on.
So the factors imho to concider are:
1) Do you like how the gun shoots
2) Does the gun meet the duty requirements
3) Do you like the weight of the gun
4) Can you carry the gun with your style of dress
In terms of the .380 vs 9mm debate. I personally see nothing wrong with .380. The bullet is basically the same thing (.9mm, .38, .357 . 380 all the same essentially). The difference is just bullet weight. When you look over ballistic charts you will see the 9mm Luger does more damage on average, but the .380 (9mm Short) still does very respectable damage against flesh and bone.
Example: (From a quick google)
Hornady 124-gr. HP/XTP (9mm)
Velocity (fps): 998
Standard Deviation (fps): 20
Average Upset (Inches): .405
Average Penetration (Inches): 14.24
Wound Volume (cu/in): 1.83
Wound Area (sq/in): 18.12
compared to
Hornady 90-gr. HP/XTP (.380)
Velocity (fps): 906
Standard Deviation (fps): 13
Average Upset (Inches): .406
Average Penetration (Inches): 11.25
Wound Volume (cu/in): 1.46
Wound Area (sq/in): 14.34
That's not a whole lot of difference. Personally, I wouldn't want to get shot with either of these. This is of course assuming guns with similar barrel lengths. The real issue with .380 is with the accuracy and reliability of the firearm. Because of their cheapness and small size, many .380 pistols really suck outside of very close range and have feeding issues (or very picky about ammo). For self defense, close range is usually all you get so the first complaint is a non-issue, but the feeding can be a real problem. So make sure you train often with your carry of choice.
Lastly, on to the OP question. You should fire some HP ammo from time to time though your weapon (I shoot it usually once or twice a year). This allows me to slowly rotate though my HP stock, to be used to the more powerful rounds (more kick, etc) that I will shoot in self defense, and to test that my firearm still likes and feeds those rounds. Anytime you buy new HP ammo you should shoot at least 2 or 3 of them out of your weapon to verify it feeds properly. Once this is done, shooting cheap FMJ ammo is fine for keeping your skills sharp.