There is really no one answer to sidemount configuration. You'd think getting a bunch of backmount divers to agree on the perfect configuration would be hard,it will nearly be impossible for sidemounters. The prevailng attitudes are 1) build it out of an old jacket style BC 2)Use the transpac either a. DiveRites recommendation b. or Bill Rennakers modification 3)out of the box armadillo. I've used the transpac configuration for years,but it doesn't look like anybody's,and is very unique,which unfortunately you'll run into a lot with sidemounters. Typically what you'll do is follow somebody's style,and modify it significantly. The biggest problem is rarely will you find anything you assemble,and ready to dive that is flawless,there is a lot of tweaking. My suggestion is to carry your question(s) over to TDS,where there is a page dedicated to this,and is visited by many sidemounters.
The system is redundant by following rules of independent doubles. You just have to have a self sufficient attitude since gas sharing is nearly impossible.