I have an 11 page paper on BPW style rigs that I provide to anyone who sends me an email address.
As others have said, for single tank diving, unless you want to have to use an STA, there are options much less expensive than the Apeks. A plate is a plate. One that has slots for tank straps coupled with a wing that also has them along with some type of roll control mechanism eliminates the need for an STA.
A harness is a harness if you go with a basic one piece. I do make custom hardware and harness setups for those who want or need them. I had a student who had a 54-inch chest. The standard one-piece harness put the straps so far under his arms that when the d rings were positioned correctly, he had no way to clip off his backup lights that made them easily accessible. The solution was to make a couple of "t" sliders that allowed the shoulder straps to be more towards the front of his body. I have since added a new angle slide that does the same thing just a bit differently. In this case, the one-piece went to two pieces of webbing plus the custom hardware at an added cost of about 15 bucks to the overall rig and he got a BPW that was functionally the same but also custom to him. If he ever decides to stop diving and sell the rig he can sell as is or replace the webbing for 15 bucks.
For single tank diving, a 30-35 lb wing will handle pretty much anything up to and including a heavy steel 95 or 119/120.
Given your info regarding your body type, and the conditions you'd be in, I'd recommend skipping the steel plate and going with aluminum since you state you tend to be negative anyway. I'd simply add a couple of trim pockets to the cam bands near the plate that would let you customize the way the rig dives, make it lighter for travel, less expensive initially, and couple that with a 32 lb wing you'd be set. Aluminum plate, 2 trim pockets, 32 lb wing with a replaceable bladder, basic one-piece harness with all hardware and crotch strap, and standard cam bands. Done.
I don't know what the Apeks rig is going to run you but I see several sites where it's between 650 and 700 bucks. That's nuts. I could put you in the rig I described above for under 400.