Congrats on your new purchase. I love my P380 and carry it every day when the weather is warm as a BUG.
I think your holster request is a challenge. Kind of hard to find a good holster that will do the double duty you are expecting. I carry mine either in a Tommy Theis horsehide IWB holster (Theisholsters.com | Home | Custom IWB Holsters) or a Mika Pocket Holster (Mika's Pocket Holsters - Custom Made Pocket Holsters, Waistband Holsters, Vest Holsters, Tactical Pocket Mirrors And Much More.). Both are great holsters that work well for me. The Theis can be worn either at the 4:00 position or in the appendix carry position quite comfortably. The Mika is an ugly duck, but it holds the handgun very securely and what I like best, is that the presentation of the grips and the draw are unparalleled in any thing else I've used. (believe me, I've tried a lot, have a box full to show you!) Both of these companies are one man shows that excel in customer service and satisfaction. Right now, they are quoting about a two to four week turn around.
Break in may be smooth or frustrating for you. My P380 took about 450-500 rounds before I was comfortable carrying. Lots of fail to feed issues and wouldn't always go into battery. Now the the kinks are worked out, I have yet to have a failure. Seems to be a very ammo sensitive gun. You'll need to find the right one for your particular gun. On the other hand, my PM9 ran well right out of the box, have had not one issue with it. Your experience may vary, but trust me, the possible agony will be worth the effort. I love both my Kahr's!
For range/target ammo, I've had good luck with the WWB semi wadcutters. Feed well and are relatively inexpensive (380 ammo ain't cheap!) Defensive ammo, I've had varying luck with. Tried Fiocchi HP's with no luck, also had issues with Speer Gold Dots. Have had good results with the Hornady FTX and Winchester PDX1 rounds. Am getting a few boxes of Winchester Ranger T HP's to try.
I've also put the rubber style Talon Grips on both the Kahr's. These really give me a better grip on the guns, wet or dry conditions. I have the skateboard sandpaper version on one of my Glocks, but sandpaper is a little too coarse for my liking for carrying on the waist. Tends to chew up any fabric it comes in contact with!
Hope you enjoy your new handgun! It should serve you well.