You can also make your own stage/pony bottle rigging quite simply. Here's a great guide DIR-diver.com - Stagebottle rigging
As for location, I'm a big fan of putting it in a place that's going to be consistent for you. I dive recreational, solo recreation, as well as tech. As such, I have my long house going down my right side, across my left shoulder, behind my head, and to my mouth from the right side of my head in rec, rec solo, and tech dives. My backup reg is a shorthose coming over my right shoulder and stored on a bungee necklace hanging at my neck in rec, rec solo, and tech dives. My pony bottle/stage bottles/deco bottles are staged on my left side in the same manner anytime I'm wearing one in rec solo and tech dives. This keeps my primary donate the same on all dives. It keeps my backup regulator the same on all dives. And it keeps my detachable cylinders the same on all dives that utilize additional cylinders. I like that consistency.
As for location, I'm a big fan of putting it in a place that's going to be consistent for you. I dive recreational, solo recreation, as well as tech. As such, I have my long house going down my right side, across my left shoulder, behind my head, and to my mouth from the right side of my head in rec, rec solo, and tech dives. My backup reg is a shorthose coming over my right shoulder and stored on a bungee necklace hanging at my neck in rec, rec solo, and tech dives. My pony bottle/stage bottles/deco bottles are staged on my left side in the same manner anytime I'm wearing one in rec solo and tech dives. This keeps my primary donate the same on all dives. It keeps my backup regulator the same on all dives. And it keeps my detachable cylinders the same on all dives that utilize additional cylinders. I like that consistency.