All non-stone stockpiles have wheelbarrows to 0, as I have 50 idle dwarves at any given time.
All stone stockpiles have wheelbarrows to the max. I subdivided some of my stockpiles into smaller zones, to maximise stone hauling.
Personally, I like to have a few wheelbarrows ready for furniture installation -- one small stockpile near the bedrooms that only holds a few items of furniture, set to take from links only, pulling via wheelbarrow from the much larger stockpile near the workshops.
With stone, I sometimes (depending on how far away the stone is, how quickly I'll be churning through it, whether I'll be using it constantly or in bursts, etc.) will start with wheelbarrows to fill it up, and then disable them once I've got a nice baseline, since having a lot of dwarves working on it may be better than fewer but faster dwarves. This has the advantage that the hauling helps to keep them in shape. (Of course, a lot of dwarves pathfinding all at once can reduce fps, but it's probably not that large an impact).
Edit: Waitasec. Am I missing something or do you have
no rock blocks whatsoever in your stockpile?
Second edit: Oh, I see, they're in with the bars, is that right? Doesn't look like you have many of them, unless they're all in bins. I'd make some more. On that note, I'd also get more bins -- with so many bars sitting out of bins, you must have a bin shortage.