I will echo a number of comments. What I read in your post is a statement of the kind of rig you are planning to have, and a question of how to acquire it in a reasonably economical manner.
BCD:
Go with a steel BP. You are planning on ocean diving. You (should be) planning on a full 3mm suit (I fully agree with Jims comment on that!). Use a steel plate and you will have minimum weight to add. I only use my AL plate when diving doubles in a wetsuit. Even if you dont know your precise weighting requirements right now, chances are a steel plate will work well for you. You can go new a DR SS plate from Dive Gear Express runs $75 or used, although it is getting hard to get much lower on eBay than the new price.
While I like the DR TransPac (and have several), given your desire to minimize added weight, I wouldnt recommend it.
Buy a 6 ft piece of 2 webbing from a LDS, and a SS buckle (NOT Trident), 3-4 D-rings and set up you own harness. It is easy, there are several threads on SB to guide you, with links to Youtube videos and other websites. You simply dont need padding. It adds to your weight requirement and is useless in the water when you are wearing a full suit. Too many divers are sold on the idea on the LDS floor.
Get a SS single tank adapter with a couple of SS buckle cam bands. Depending on the wing you choose, you may not need the STA, but having it gives you some additional flexibility in wing choice.
Wings: you will find little difference in wings across a variety of brands. I happen to use a Halcyon 30lb wing, but I got it at a shop staff (discounted) price so it was modestly priced. New
H equipment is a bit pricey. A ~30lb donut should be fine. I really like the Oxycheq Mach V but dont expect to save money on a new one, and used ones are scarce. DSS markets a 26 lb Torus donut wing that is very nice as well.
Regs:
The Apeks regs are a very good idea. And, kudos to you for going with equivalent primary / alternate second stages. Scubapro is fine, too, no better than Apeks. You can usually find used ATX / XTX 50s on eBay if you are willing to be patient, and that would save some money. But, buying them new is also a reasonable investment. They will last a long time and accommodate your continued diving development.
Computer:
PfcAJ:
Don't bother with a Zoop . . . Grab a Uwatec Digital Depth Gauge for 100 bucks and be set for life.
In principle I agree with the idea of a digital depth gauge it gives depth, time and temperature which is really much of the value of a computer for recreational diving, anyway.
But, a new Zoop costs about the same as a new Uwatec DDG. Yes, you can wait and try to find a used DDG but generally the people that have them like them and use them, so they dont come on the used market that frequently. Or, if they do they are either quite mature or not fully functional (which is the primary reason someone gets rid of theirs). If you can find one cheap, fine. But $250 for a Zoop isnt bad.
SPG:
I agree with the comments that $125 seems pricey, although that may be the price for a gauge AND HP hose. A simple XS Scuba 2 or Thin Line SPG should be fine. Dont go console. Start out the right way and you wont regret it.