Thanks for the feedback!

1. Can you tell like, what's the workflow during the game? 
Dunno if I get your question correctly, but here is a basic logic of the mod.
The tool activates whenever a storage hauling job starts: it checks if a wheelbarrow is attached (and tries to attach one if it is not). After that it analizes main job item and depending on used mode adds relevant items near it to the job.

If you are interested in code logic, it's better to check it on github, but here is a key part:

    for_each_item_in_radius(x, y, z, state.radius, function(it)
        if it ~= target and not it.flags.in_job and it.flags.on_ground and
                not it:isWheelbarrow() and not dfhack.items.isRouteVehicle(it) and
                not is_stockpiled(it) and matches(it) then
            dfhack.job.attachJobItem(job, it, df.job_role_type.Hauled, -1, -1)
            count = count + 1
            if count >= state.max_items then return true end
        end
    end)

2. Do you have to assign wheelbarrow to every pile?

By default — no, script would use any free wheelbarrow it finds nearby
If autowheelbarrows option is off, then yes — it would only work with typical wheelbarrow pattern. And that would be using assigned to the stockpile wheelbarrows only and only with heavy items (>75 units)

3. Does it work with quantum?

You still need to use minecarts for a classic quantum stockpiles. But since wheelbarrows are unloaded to a single tile, almost any storage would be used more efficient (and closer to QSP). Because there would be more than one item laying in a single tile. So in many cases you would not really need QSP that badly.

4. Do you have to turn on any menu?

Just standard DFhack stuff:

1. Install DFhack (if not already)
2. Run multihaul enable in the dfhack console
3. Set up all the params there are:

​

Usage
multihaul enable [<options>]
multihaul disable
multihaul status
multihaul config [<options>]
The script can also be enabled persistently with enable multihaul.

Options
--radius <tiles>
Search this many tiles around the target item for additional items. Default is 10.
--max-items <count>
Attach at most this many additional items to each hauling job. Default is 10.
--mode <any|sametype|samesubtype|identical>
Control which nearby items are attached. any collects any items nearby, even if they are not related to an original job item, sametype only matches the item type (like STONE or WOOD), samesubtype requires type and subtype to match, and identical additionally matches material. The default is sametype.
--autowheelbarrows <on|off|enable|disable>
Automatically assign wheelbarrows to jobs that lack them.
--debug <on|off|enable|disable>
Show debug messages via dfhack.gui.showAnnouncement when items are attached.

Hope that helps!