If your USPSA belt rig is the usual dual belt setup it's definitely a no go
If your holster is significantly offset away from the body and/or dropped to where the front strap of the pistol's grip falls below the top of the belt, definitely a no go. Read the rules carefully on this.
I shoot IDPA SSP with the same pistol I shoot in USPSA Production.
I use a simple kydex OWB pancake holster, my every day CC belt (Ares Gear), and a couple of kydex clip-on mag pouches (same kind I use for CC).
Speaking of magazines and pouches, you won't need as many as you do in Production. There's a limit to how many you can have on you anyway and it's a lot fewer than five.
At any rate, the course design rules are such that you won't need more than two mags (if shooting ESP or SSP) to complete any stage. I start any stage with three (the most allowed in SSP), two on the belt and one in my front pocket that goes in the gun at make ready.