I utilize SERPAs with the paddle attachment (can't remember if they're CQC or not) for both my pistols (Springfield XD subcompact, Rock Island Armory 1911). They work fine, retention is enough for my peace of mind, and since I'm mostly carrying between work and home the paddle makes disarming easy enough.
As for the mag holster, I don't have Glock-specific recommendations, but I'll tell you about the two brands of mag holsters I have and take it for what it's worth. For my double-stack XD magazine I bought a Galco "Concealable" leather mag holster. http://www.opticsplanet.com/galco-co...zine-case.html The friction is strong enough that I've never had a mag fall out, even while playing with my children. For my single-stack 1911 mag I bought a Galco CLMC Carry Lite http://www.opticsplanet.com/reviews/...magazines.html, with the intention that I could remove it (via the snap) without removing my belt. In reality, the snap is so freakin tight that I gave up on it, and just leave it on my belt even at work. (It's unobtrusive enough that only "gun guys" notice it's a mag holster.)