Mate from a Euro / Australian perspective, there are two payments after your reservation:
1. $5000 round up to secure your purchase. Then in the fullness of time you will then get your contract. Keep in mind the timing of this has been all over the place. In theory you should get it just before Ineos starts your build, so maybe 3-4 months before you get your car. In practice it has been somewhere between 6 months prior to build, to after it's been built. No doubt this step is a work in progress.
2. Just prior to delivery you will be contacted re final payment. Those in Europe have had to pay Ineos 48 hours before delivery. My intention is not to pay until the dealer confirms it is in the yard, has had it's PDI done, and is right to go defect free - a number of guys in Europe paid and then had to wait weeks for their vehicle (very poor form). In Australia we are also used to not paying until we pick up the car, so I'm not sure if the 48 hours thing will work, particularly for those who need finance.
Hope this helps.