When creating a new order (on the dashboard) how can I get the ID of the selected customer

When you hover over an user edit profile you can know their ID.

For getting Alpha and Beta value.
Since the order is not saved you can’t get any value. You need to save the order with Alpha, Beta values through meta boxes input interface.

If you wanted to get the Alpha, Beta values for already created order then you need to get it through

get_post_meta() function with post ID which is order ID in here