I would like to include a deposit option and then when the same customer returns they only pay part.

I believe that can be achieved by using two forms. The first form will collect the deposit, and the user will receive a link to the second form. When they open the second form using the link, they will be able to see the remaining balance that they will need to pay with the help of sessions. You can check out this thread that will walk you through setting it all up: Is there a way to accept a deposit payment, and then pay a balance due at a later date?

Alternatively you can also setup a recurring payment that will initially charge the user for the deposit, then it will charge them again at a set time depending on the subscription period you have set. Please follow this guide to set it up: How to setup a recurring payment option

If you need further assistance, please let us know.
Regards.