Fix Opencart Cheatout Process

There is an issue with the checkout process for my site. Here are the 2 things: 1 - after a person submits the order, it doesn't automatically empty and refresh their cart. They aren't rerouted to a thank you/order confirmation page. The only thing that happens is a small box pops up saying "Your order has been received". This is causing numerous duplicate orders and upset customers. I need this fixed. 2 - customers who have an account set up, when inputting an address aren't required to fill in the post code. This is an absolute must. Also, the zip code doesn't address in the display address line. I need the zip code to be require and displaying.