I don't own a P345, but I do own a P90.
I am pretty sure those are two completely different firearms in every respect other than the name "Ruger", and the caliber, so I don't think any experiences I can share will really help you - but since no one has answered you, I'll throw it out there anyways.
1. How many rounds have you shot through yours?
2. Any misfires?
3. What ammo do you use for practice/defense?
4. How do you carry it - holster/placement.
5. Any major issues?
1. approx. 1000
2. no failures to fire, feed, or eject, ever, on any ammo used (see below). One point - I am pretty sure the P345 uses an integral feed ramp, as does my P90. I have been told by two gunsmiths that feature helps assure reliable feeding. I don't know that to be fact, just what I was told, and I have had no issues.
3a. practice - a wild assortment of WWB, Federal, Blazer Brass, S&B, Rem FMJ (and others that I found here and there)
3b. SD - I have a small assortment that I have tested - Rem/UMC 230 gr HP, Rem Golden Saber, and it is loaded with Hornady XTP +P 230 gr (mainly because that is what I have the most of currently that has been tested by me in this gun).
4. I don't - this is my nightstand pistol.
5. No issues at all - I love it. All I added was Hogue grips. It's also heavy enough that if I run out of ammo I could open a skull or two with it.