Set Customer Payment Permissions

Our customers are on a term of 50% paid when ordered and 50% on delivery. For new customers we want 100% charged until they're established

There's not a setting for 50% due upon order and 50% upon delivery but maybe you can find a compromise between pay up front and having a grace period... Here's how you'd take care of the rest of it - since you want all new customers to default to paying up front you'll need to set that in your financial settings. Do that by going to Settings -> Financial and then set "Default Checkout Flow" to Pay Before Proccessing (see below):

Then in the company settings for each individual customer you can override that default for those that you want to have the 30 day grace period. In that case you would change their checkout flow to User Credit Limit and then be sure to set a credit limit and/or build limit, choose the order status you want the invoice to be "due" and then the desired grace period (the time between when it's "due" to be paid and when it will start accruing finance charges). See image below which is in company settings for a customer: