Slow and steady is fine for screwcutting, but what about turning down to size and crowning, etc,? Btw, slow and steady is all my treadle lathe does!
How would you calculate the weight needed to counterbalance? (it's a bit like a pound of flesh type calculation, surely?)
3 jaw chuck and shims or 4 jaw chuck (which I don't have) is easiest, surely?...it holds the breechblock securely so that the offset mass of breechblock makes very little difference.