Is your barrel new or used? Is it intended for wine/spirits? Do you keep it filled with water between batches? Did you sanitize it before adding the cider? Was the cider "harsh" before it went into the barrel? You mentioned it might be closer to wine than cider due to a high ABV, what was the ABV? The higher the ABV, the longer it's going to take for the flavour to mellow. How long was it in the barrel?
As for your questions on yeast: I've switched to ale yeast for apple cider, it tends to produce a slightly sweeter, better balanced cider; I use Nottingham, but there are several choices out there that are good. You might find this informative:
As for your sugar questions: I'd stick with 2lbs/5 gallons, for a total of 22lbs for your 55 gallons. As far as the type of sugar goes, it's pretty much wide open.
People have used corn sugar, cane sugar, beet sugar, honey, light and/or dark brown sugar, molasses, maple syrup, demarara sugar, malted grain, malt extract, etc, etc...
The thread linked above will cover some of these various sugars. For more check out the recipe section:
You might also find some answers in the "I love apfelwein" thread, but it's a looooooong one: