Hi Ian, The XF Sportbrake (Estate) is a great car and really spacious - my daughter has one.
In my opinion, go for the petrol engine, unless you plan on travelling over 15,000 miles a year in it. The petrol engines are so much more refined than the equivalent diesel and you should have nil worries about Low Emission Zone compliance.
Highest specification is always a target, maximum number of toys, etc. although they are generally well appointed.
Come back if you have anything specific you need to check, otherwise happy hunting and let us see the photos when it arrives.
N6 JMX