Now I am a bit of a minimalist as it is, and this BP/W things sounds nice, but I have one issue with it. I dislike weight belts, and I am a floater, always have been. In a Full 6.5m Farmer John I require 30lbs to sink. In a 6.5m Shorty 14lbs...this is in fresh water. I also like the idea of SOME dump-able weight, which with a BP/W sounds like it isn't that hard to add. I am not talking a lot of dump-able weight, maybe 10lbs.
My weighting is correct and I use an Ali BP, 3mm full suit and need no extra weight. If I did need extra weight (sometimes when diving with multiple stages), I can happily put a few lbs on a weightbelt.
However,
if you do need that much weight then the modular design of BP&W configurations will give you options.
You can buy ready made integrated weight pockets that fit onto the waist-band of harnesses...and also trim weight pockets that fit onto the cam band (if diving single cylinder). You can also buy weights that bolt onto the backplate or between double cylinder set-ups.
So where do I start assembling a BP/W setup? Obviously I can check with my LDS, and I will, but is it a situation of all Back Plates fit everyone, just pick a Single vs Double?
You can buy them ready made. Google for brands such as Halcyon (model: Eclipse), OMS, Dive Rite or Oxycheq to see your options.
The BP is universal - for either single or double cylinders, although they can be offered in varying sizes, weights and materials. Most people opt for a standard size made out of steel.
Harnesses come in varying designs. Some are more akin to conventional BCD systems...with adjustments, quickrelease buckles, fixed d-rings and padding....others are just a simple, single, piece of webbing threaded through slots in the backplate.
You choose what is most appropriate for you.... but most divers tend to gravitate towards the more simple webbing design. This is because it is easily (and infinitely) adjustable, simple, uncluttered and cheap/easy to replace. The option of one or two quick releases on the shoulders benefits some divers, although is by no means necessary unless you have mobility problems in your shoulders/arms for getting into and out of the harness.
Despite 'appearing' uncomfortable, the metal backplate does not require the addition of extra padding for most divers.
I imagine the only thing to worry about fit on is the Harness..which I take it is also called the Webbing.
As I mentioned, you can either buy a harness with adjustments and releases....or a simple webbing 'belt' that threads through the BP. You adjust that belt to fit you (as it is threaded through the BP). As such, the adjustment is infinite....you just get a sufficiently long length of webbing, fit it, adjust it to fit and then cut off the surplus.