Create and confirm a Sales Order for 10,000. (you may want to use the Unreserve feature on the Delivery Order if are using inventory reservations - which are active by default).

When they are ready to place their first order, add the regular priced items to the same Sales Order and split the Delivery Order according to how many of the 10,000 they need.

Repeat the process until they have received all 10,000.

The Delivery Order each week / two weeks (after each split) will contain the regular priced items plus the quantity of the 10,000 they are choosing to get each week / two weeks.

You can then invoice each week / two weeks based on just what was delivered.

Hi,

another way to find a solution that will take into account the fact that you have 10000 units with another price.

You create a specific "Loyality Cards" (ex: "Special Price for 10000 units preordered"), 

• set a limit usage to 10000.
• Make a reward as a Discount on your specific product only.
• Set a condition to  mimum 1 paid & grant 1 loyality point per unit paid.

Create a Loyality card for your specific client and set the amount up to 10000 in his balance points.

The weakness is you can only make a discount pourcentage on the product price

Hope it'll work ;-)

Ciao Chris
puoi provare così:

Crea da Prodotti>listino prezzi  un listino dedicato per questo cliente con tutti i prodotti che vendi

poi sempre dalla stessa posizione crea una regola per il prodotto che hai quotato, inserendo le quantità minime e la data di inizio e fine offerta.
Penso possa funzionare.

Fammi sapere