It may help to add a related table to orders where each record is a different date or date range when the ad is to be run. A portal (think subform) on an Orders layout would then list all the scheduled times as a series of rows in the portal. This portal, or the related table would be easier to search in order to find all the adds scheduled to run on a specific date or date range.
There are several ways to set up what you want to that selecting a client causes other fields to display data from your cliients table.
Option 1: the data is a "snap shot" physically copied from clients. If client data is later updated, this "snap shot" will not change.
Option 2: the data is dynamically linked, any future changes to the related table's data will automatically appear on your layout.
Option one uses "looked up value" field options set on matching fields in your orders table.
Option two simply requires placing the fields from clients on your orders layout.
Both options require that there be a correctly defined relationship linking the two tables. Setting up a ClientID number as an auto-entered serial number in clients is your best choice as a primary key for this table. Linking it to a matching number field in orders is all you need for either of the above options.