3 things - does it work, is it safe, and is it efficient? Everything else is icing on the cake... or personal opinion.
On the subject of personal opinions...
-I hear the GGG frog harness is great (although I use a Petzl one personally)
-A steel half-round Maillon Rapide is fine, but I prefer a Zicral (aluminum) one, or that new Petzl Omni half-round carabiner (which is big $$$)
-The Petzl Stop is a fine choice. Think about trying the Petzl Freino as an attachment/braking carabiner
-If you use muddy swollen ropes *a lot* on short-ish drops, you might want to think about a micro-rack with hyperbar instead of a Stop
-The 8mm cowstails should be fine, assuming they are made of dynamic rope rather than accessory cord
-The Croll - no contest there
-Jumars are fine, I used one for many years before switching to a Petzl Ascension. The Petzl is a little lighter and slightly easier to use, but the original Jumars are a solid piece of kit
-The 8mm footloop might be overkill - a 5-6mm spectra/tech cord footloop is stronger, more compact, and has NO stretch (which does help)
-The QAS - it's a Frog system, so technically you only need 2 ascenders. However, carrying a third gives you lots of options and is certainly a good idea. I carry a little Petzl Basic, which I can clip onto my adjustable-length cowstail if I need to.
-The Petzl chest harness is OK, but I prefer the GGG design. It takes a little longer to untangle and put on, but it's more supportive than the Petzl ones without irritating your neck
-Using a right-handed Jumar as your handled ascender is fine, assuming you're right-handed and/or that's your personal preference
From what you described I'm sure your system works, and is probably perfectly safe and reasonably efficient.
Cave safe!