I just picked up a SIG P320 [compact frame, 9mm], so now I need to learn about it.  So far it shoots real nice, and quite accurately.  
I ended up with 3 mags, and SIG even tossed in a Kydex (ish) holster.  It seems the mags fit fairly well in my XD magpouches, buit since they are only 15's, they did seem short compared to my XDM's 23 round (with basepad) mags.  

So now I am looking at stuff for the pistol.  I think I want a dozen or so extra mags, 4-6 mags worth of mag pouches, a nicer holster with retention, maybe a new light, and maybe even a replacement frame to stipple the heck out of so I can shoot it in a match...so on it goes...

Tell me everything, is there a part I need to plan on replacing or having replacements for?  Where is a good place for accessories (extra points if you know of a SITE SPONSOR that has things like mags in stock for a reasonable price)...

Carry or Compact?

I did not know the compact model was out yet?

I have the P320C (carry) model. On the frame it says "compact medium". So I guess you could call it either one?

The way I understand it, I have the Compact, which is the mid-sized frame and slide.  I believe there is one size each larger and smaller than what I have.  Mine takes 15 round mags.

My bad...I was thinking subcompact when I wrote my response.

there really isn't much of any gear support for the P320 yet. Mags, extra grips, and holsters for the P250 will work. I bought some mags from Top Gun Supply and got a kydex holster from KT Mech. I don't know of anyone offering any replacement parts for the P320 yet, Sig doesn't even offer any for sale in their store. If you want a trigger job done the Sig Armorer(not the factory) does then.