Side,
sorry to ask about the front-end loader .....the filter at MY workplace "bans" most pictures that are not embedded into the post..(ONLY seeing your pictures for the first time at home!) And I assumed that you were asking about a spear attachment to the front end loader
To answer your question better than I did before - as for weights on the front end, I would imagine that you could place anything from 100 kilos to 250 kilos if you have weight to place.
your machine weighs in at about 2000 lbs without any attachments. SO picking up a 1000 pounds on the rear - you would want weight on the front too.
Typically a tractor has as a loader up front and weight is added at the rear so the tractor has traction at the rear and so that the rear does not come up when the load up front is too heavy. In you case, you are doing just the opposite.
Here is what I would recommend - find the amount to place on the front that is not too heavy, something you can leave there and be able to use the tractor with the bales on the rear - yet once the bales are loaded on the rear, it will be enough weight to offset the bale itself.
You have 100 kg now - how does that work? IF not well, add more till you find that amount that works the best