Absolutely a bpw regardless of if its a Halcyon or not is wortht the cost even for a new diver. Especially for a new diver. You will become a better diver than most of the people in your class more quickly in a bpw and I will guarantee that pretty much no one on any board that made the switch to bow regret the decision or disagree it will help your diving progression. I personally as I've stated before believe your the perfect person to gain from the cinch system. You are unsure in your diving future and will be diving many different environments with varying levels of exposure protection. The cinch will simply make the transition seamless. Get on the boat or at the dive site, loosen the shoulder webbing, climb in, tighten, dive. No adjusting the triglide slides base on your exposure protection. It simply makes your life easier, and I don't believe you'll be unhappy with it. In my doubles because I likely will always be in a drysuit, I really didn't need the cinch because I liekly wouldn't need to adjust because my protection won't change. I still got it anyway simply because I love the ease of getting out, plus if I do decide to dive wet, I don't have to adjust again. I plan on getting into deco procedures eventually and after two to three hours in the water in doubles with stages I'm going to want the easiest way out of my harness when I'm beat. The way I look at it, unless you know exactly what your diving will be in 10 years, then buy gear that will grow with you. In my opinion the cinch allows for growth, so I buy it on all of my Halcyon plates.
As far as the face down at the surface, yes absolutely any back inflate be it a rec bc or a bpw will put you face down when you overinflate. The problem is that most new divers are uncomfortable at the surface so they overinflate to get way out of the water, which will tip you forward. You will soon learn how much to actually inflate so this doesn't happen. And don't worry its not puching you uncontrollably face down, it just leans you forward. When you feel it, let a little air out. Again any back inflate will do this, not just a bp.
And lastly, backplates are not technical rigs. They are the preferred rig for tech divers, but they are for any stage of diving. And more and more people are learning how amazing a bp/w is. My OW and AOW instructors were nontechnical(this was 17 years ago) and felt anything other than a good old BC was tech. It was the biggest damage ever done to my diving. I've dove a bc for 17 years. Once I got into a bp, it transformed my diving, from swimming undrwater, to flying gracefully underwater. The comfort and control I felt in the bpw is what gave me the confidence to pursue technical diving. I was not a tech diver or planning to be a tech diver when I bought my bp...