1.) DSS, BP/W, and Tobin's short inflator hose
2.) BP/W and a weight belt makes it hard to ditch weight if ever needed
3.) Slight over weighting as a beginner?
4.) Proper weight distribution
I got a DSS BP/W immediately after I finished my OW cert. I never had any in-person assistance with getting it to work for me. Only what I found on the Internet. Mostly, very helpful advice from a few people on here. I never had any trouble with it, but my comfort with it did increase gradually over the first 20 or so dives, I guess. The improvements in comfort mostly came from the fact that my harness was initially much tighter than it is now. I could put it on (on land, with no tank) and fit my fist through the shoulder straps like "the directions" say you're supposed to, but it still was too tight. With it too tight it was a bit difficult to don/doff. And my trim was further from ideal than it is now. Once I finally got it to where it stays now, it is loose enough that I can put it on easily, on land or in the water. And I can take it off in the water easily, too. I did my Rescue class using my BP/W. When it came time for the exercise where I was towing a diver, giving rescue breaths, and simultaneously supposed to take my rig off, my instructor said something about swapping me to an integrated BCD for that exercise, so that I would be able to take it off. I said no way and did the exercise, easily getting out of the rig while towing and simulating rescue breaths. I could not have done that with my rig adjusted that way it was when I first started using it.
I am 6' 1" and my chest is 10" bigger than my waist, so, according to the men's garment industry, I am somewhat barrel-chested.
I have the stock 16" inflator. It hangs just over and past the top of my shoulder. With it there, I have no trouble reaching it or operating it with my left hand - in any orientation underwater or on the surface. If yours doesn't hang over that far, it sounds like your BP is too low on your back. If your problem is simply doing it using the "form" that they taught you in class, well, do what works for you and don't worry about the Official PADI Inflator Hand Position. If yours does hang over your shoulder and down your front just a little bit and you really just can't reach it, then it sounds like maybe your cold water gear doesn't fit right and is binding your left arm way too much. Imagine yourself wearing a set of doubles. Even in full cold water gear, if it fits right, you would be able to reach back to your tank valves and the isolator valve. And if you can reach those, reaching your inflator should absolutely be no problem.
Your concern about your weight belt seems to be that other people won't be able to get it off you in a rescue situation. Okay. Wear it over your crotch strap. Or put weight pockets with quick release deals on your harness' waist belt. But, note that a lot of experienced divers have now said that they don't worry about having ditchable weight. Personally, I'd say to try wearing your weight belt over your crotch strap until you feel comfortable enough to make a decision for yourself on how you want to change what you're doing.
Some people will probably say (or at least think) that I am ignorant due to my relative inexperience on this. But, when it comes to weighting, I feel like "proper" weighting is being able to be neutral with an empty wing and an empty tank - all while you are breathing normally. When you are new and don't have breathing control that is as good as it will be later, that means you'll carry a little extra weight. But that doesn't mean you are over weighted. That means you are properly weighted - for your current level of experience. In other words, however much weight you NEED is what is proper. What you NEED should reflect an empty wing and an empty tank and whatever level of breathing control you have - not what you will have at some point in the future.
Also, an AL80 carries about 6 # of gas. With 500 psi in it, that means it should still have about 1# of gas. So, if you are weighted properly, you should be at least 1# negative at a normal safety stop, regardless. Thus, if shtuff happens and you need to hover at 15' until you literally draw the last gas from your cylinder (because something happened and you stayed down too long), you can do so without having to fight to stay down (or corking).
Say you weren't paying attention and you suddenly realize you're still on the bottom and only have 400psi left. You do a controlled ascent to your safety stop, but don't have enough gas left to stay for the full 3 to 5 minutes. You still want to be carrying enough weight that you can stay at 10 or 15 feet for as long as possible. An extra 1 or 2 minutes there really does make a significant difference in your chances of getting DCS (if you were anywhere near your NDL).
Any gas that you are carrying without weight to counter balance it is useless, really. It's serving only as ballast. You may as well carry less gas and replace it with lead. At least you'd have a chance to easily ditch lead if you had to.
In other words, I say, do what works for you. If you need an extra 1 or 2 # to be able to stay down even if your breathing gets out of whack for a minute, then take the weight. When your breathing control improves, you can shed the extra weight. An extra 8 or 10 # would be bad. An extra 2 or even 4 # beyond what you absolutely need just isn't a big deal.
For trim, the weight should be wherever it needs to be to let you achieve good trim. If you have trim weights in tank strap pockets, make sure those pockets are tight up against the back plate. If they are and you still feel like you're getting pulled over backwards, move the trim weights to your front. Or sides. Whatever works. Just be aware that what works best for you may change as you develop your skills and experience.
When you can hover perfectly horizontal, with good form, and perfectly still - not moving your hands or even your fin tips - you will have found Trim Nirvana. Wherever you need to put the weight to do that is just where it needs to go. From there, you may possibly tweak it by moving weight from your back around to your front, if you want to change your balance when you are in non-horizontal positions. But, I'd bet that by the time you are able to hover horizontally and perfectly still you won't need any advice from the Internet on where to position your trim weights.