Multiple payments on same order

[stralis]

I have a business where I make tailor made paintings. In my business model I want to accept a 20% down payment and when when the customer are OK with what he gets, he pay the rest and I deliver his painting. I'm have been looking at both version 1.3 and 1.4 and right now I'm using vesion 1.3.1.1

Is there a way to configure or modify Prestashop so a customer can pay part of the order up front, and pay the rest later. In my case it will be two installments. A 20% down payment and 80% on delivery. Should I set up 2 different products, one called 20 % down payment of the product and call the other 80% final payment of product.

Since the down payment doesn't include any shipping, it should be an order without shipping like a digital product. This setup is not so good since it's so easy for the customer to pay for wrong final payment. This setup is very confusing for my customers so I wonder if there is a smart way to configure or modify Prestashop so it's possible to accept two different payments for the same order and make it easy for the customer to understand what to do when it's time to pay the final payment?

I would like this to be an option for the customer to make a two step payment (first 20%, then 80%) or pay everything right away, like in the normal payment flow. It would be nice if the customer could go to his account and see status of order "not fully payed" and choose to do the last payment.

Any idea how to setup this payment flow that fits my business?