Try moving a few kg up to the camband. You can get pockets which thread on to the camband which are perfect for this, and make swapping the cylinder over much easier.
My own revelation was on a course a few years back. I put my 15l cylinder in for a fill, but someone in another group picked it up. Fortunately one of the instructors on the event had a spare cylinder which I borrowed, although it was only a 10 litre cylider.
By some pure fluke, this put the weight right in the middle of my back, and I was able to float, godlike, in horizontal trim. I put my 15l on the next day (it turned up over night) and then I was fighting the kit for the rest of the dive. I then started moving the weight around inch by inch until I was trimmed neutrally.
Fast forward a few years and I've a few more dives under my belt and now the weight distribution is less critical. I can trim most sets of kit out by moving feet arms and legs. So - I was spend a bit of time faffing with weights and improving your trim, but use the weights as a gross adjustment and fine tune with your body.
For BC vs wing, I don't think it matters that much. You're only going to have a couple of litre of air (so 2kg) in it and you need to put that into the context of whatever you have on your weightbelt. Go for whatever you like the look of and is comfy. If you can try it out a few times beforehand then so much the better.