Can anybody figure this out?

I think the proper term for the "Starter" may be "Sponge". A lot of these terms are bandied about rather loosely. I have heard the phrase "Pre Dough" and "Autolyse" also used. "Starter" usually refers to a natural levain (commonly called sourdough starter") and is a culture of natural yeast, as you already stated.

I would make this recipe by mixing the "Starter" and letting it sit for 6-24 hours at room temp ( about 65-75 F). Then I would mix the final dough. The resting,mixing,kneading or stretch and folding are up to you. Try one method,document it,decide if you like the outcome and adjust the process on paper. After a few tries you should have a process you like.

I did not do any analysis of this recipe in terms of hydration,etc so I assume this is a do-able ratio of ingredients.

The "sponge" has no leavening.  The final dough hydration level is about 36%.  The salt is 0.14%.  

The sponge hydration level is fine; something north of 100%.  However, if it really is a sponge instead of a soaker, I'd probably stir in 5-7g of instant yeast or 50-100g of sourdough starter to leaven it.

The final dough will need at least 9kg of water, rather than 3.5kg.  If the flours are whole grain, rather than white, you might want to aim for 10-12kg of water.  Salt should be around 1.5% of flour weight, or 200g.

I'd mix the starter ingredients (including leavening agent) in the evening and allow to ferment overnight.  On the next day, I would combine the final dough flours and water and let them autolyse for half an hour or so.  Then I would mix in the yeast, followed by the salt.  There's enough wheat flour in the formula (47%) that kneading of some kind (not stretch and folds) for a few minutes would be beneficial.  The bulk ferment until nearly doubled, shape, final ferment and bake.   

There are a lot of rye bread discussions on the site.  After looking at them, you'll probably see some with similar proportions of ingredients and be able to select shaping and a baking profile that suits you.

Best of luck!

Paul

I agree with Paul, the "starter" is probably a soaker or mash. So you can let it sit with room temp water for 6-24 hours as clazar123 suggested; OR, if you want to coax additional sweetness and shorten the time, heat the water to boiling and mix in the flours to scald the "starter", let the scalded mash rest at least 2 hrs (or up to 24 hours) then use. 

Doesn't appear to be a sourdough, because there is no leavening in the 'starter'.

If you wanted to make it into a sourdough, you would need to add some sourdough to your 'starter' (maybe 200-400g of active sourdough starter), let it ferment until bubbly and just barely starting to collapse on itself, then mix it with the rest of the bread ingredients and continue to process (mix, rest, knead til developed OR stretch and fold, let rise, shape, let rise again, bake).