Here is my stab at your questions:
Halcyon equipment tends to be at the pricier end of the spectrum. It is nice stuff but whether it is worth the expense is something that you would have to evaluate for yourself. Often the price of Halcyon gear is referred to as the "H" tax. I believe there are more affordable options of high quality gear on the market. Figure out what your budget is and then find brands that are within that range.
The major choices for backplates and wings break down to the following:
1. Material choice for backplate - typically the choice is between stainless steel, aluminum, and soft plates, though ABS plastic, Kydex plastic, carbon fiber and titanium also exist).
In my household we have stainless and aluminum backplates. I have no experience with soft plates. I also believe that an aluminum plate would provide more durability and a better price for similar weight compared to kydex, carbon, plastic and titanium plates.
If you are diving in cold water with a thicker exposure suit, the increased weight of a stainless plate will be of benefit as it shifts ballast around your center of mass. If you are traveling to dive a lot the lighter weight of an aluminum plate may help keep your baggage fees to a minimum.
You can certainly travel with a stainless steel plate to dive warm waters. It will not be too negatively buoyant, but it will most likely provide more ballast than you need depending on your body composition, residual lung volume, exposure suit choice, and other factors. If it is providing more ballast than needed it will be comfortably spread out over your center of mass and you can compensate by adding air to your wing.
Aluminum plates, 2-inch webbing, and some d-rings and tri-glides are not that expensive, so if you find that you are traveling a lot you can easily and affordably put together a 2nd backplate/harness to accommodate your dive plans.
2. Type of harness - typical choices are between a single continuous length of webbing vs. harness setup with separate waist and shoulder straps. Also padded vs. unpadded.
All the plates in our 4 diver household use continuous length of webbing (hogarthian style). My reading when first venturing into backplates was that there was a tendency for folks to buy fancier harnesses with adjustability and padding only to eventually migrate to a simple single continuous length webbing harness.
Comfort, delux, and multi-piece webbing harnesses are a good option if you have mobility issues with your shoulders, but my reading of others' exprience beyond mobility issues is that folks don't adjust their harness as much as they thought they would making it an expense that was not needed.
Another aspect of adjustable harnesses to think about is that often there are metal bits sewn into the webbing bits. The proprietary nature of this means that you either have to source replacement parts as the webbing wears out which can be at quite an expense, or cut out the metal bits and sew them into new webbing yourself (or hire someone to do it).
The simplest and least expensive option is the single length of webbing...it is also the most customizable with regard to placement of D-rings, pouches, what-have-you, as there is less to encumber your choice of where to position things.
3. Wing lift amount - for single tank wings the options are predominantly in the range of 18lbs to 32lbs of lift, though there are wings that have less and wings that have more lift out there. The shape of the wing has been of increasing focus as well.
The argument for wing size is that one should avoid a wing sized in excess of their needs to avoid excess drag in the water. For instance, it may seem more affordable to buy a smaller wing designed for double tanks or designed as a hybrid to use with both single or double tanks, but often these wings are not big enough for the needs of double tank divers and often are too big single tank setups....they tend to taco around the tank when inflated causing difficulty in reaching the lower rear dump valve, and causing drag due to the excessive material of the large wing.
The last few years has seen increased discussion on streamlined designs of single tank wings along with a mentality that leans towards a minimalist amount of lift. There are various rationals driving these gear choices, some well reasoned and some not grounded in reality at all.
For your body weight (200lbs), exposure suit (7/5mm), and experience level, I would recommend you get a wing with 30 to 35lbs of lift. The physical size difference between a 25lb lift wing and a 30 to 35lb lift wing can be argued as being negligible underwater (all other design factors being equal). For lift amount of the wing you need to decide where you will wear your additional ballast such as on your body via a separate weight belt/weight harness or in pockets mounted on the harness, plate, or tank straps. Your wing needs to provide enough lift suppport you and your gear on the surface....if all your ballast will be mounted on the rig you may find that you need a wing towards the end higher lift capacity spectrum to accommodate keeping it afloat at the surface without you strapped in to it.
My personal opinion is that a wing in the range of 30lbs to 32lbs of lift is more than adequate in most single tank situations and provides a margin for adapting to the ballast requirements of different exposure suits and water temperatures without being excessive in dimensional size.
All other choices are pretty much about how you want to customize your setup such as how many and where you want to position D-rings, pockets, etc. As mentioned above the simple single continuous length webbing provides the most amount of customization in this area.
For customer service, Dive Rite, Edge-HOG, DGX, Deep6, and DRIS are notably excellent among the many companies and retailers that provide good customer service and support. There is little to go wrong with a backplate and wing, and the modularity of the design makes it easy and affordable to modify and replace worn out components of the system.
I hope this helps and if you have any more questions, or if I failed to address any of your current questions/concerns please let me know in response here or by private message.
-Z
