$339 is a good price. Today's Cabela's tab has them on sale at $389 in "my" store. (I refer to my trips there now as going to the holy land.)
Someone's rule of thumb, but more for competition than everyday carry, is 10 magazines. I'm not quite there, but I do have 6 for my carry gun and will get to the 10 level soon. It makes rotation easy. Load five of them, (1 in the gun, 1 carry, 1 in the car and two in the Get Home bag). When you go to the range, shoot those, then put them aside and load the other 5. Simpler than Cooper's rotation schedule.
I have 12 for my Glock but that's because it means I can shoot two entries in indoor league without reloading.
Glad you got the LCP. Of the pocket sized .380s that's a good one. Just stay away from Taurus. Been there, done that.