as far as i know, you can only configure the “Site” to be mandatory , it’s done in Inventory management > Setup>dimensions>dimension groups. however the user will still be able to create a sales order without selecting a site in the create order form, but the order cannot be posted for picking/packing/invoice unless a site is specified.
and about the delivery term and mode, you can only set up default values for every customer, this way they will automatically load on the form when an order is created for the customer.
the only way to force the user to make selections in those fields before closing the Create order form is through the AOT. if you found another way please share it.