Hi Glenn,
Welcome to the forum. Your in the right place.
The Premier spec has the Mark Levinson system, the F Sport does not unless specified. The main difference between the F-Sport and Premier is looks and the F-Sport has the fancy (LFA) style instruments.
I have a 2015 Advance model that has standard sat nav and sound system, but nice heated, cooled, electric leather seats. No sunroof. Road tax is £10.
Premier is best if it is in your budget as it has Mark Levinson and the toys. F-Sport if you prefer the looks. Try and find an F-Sport with the Mark Levinson system upgrade. Check the car tax as some models may be in the higher tax bracket as the cost new was over £40K.
I currently get around 45 mpg on short (8 mile) town commutes.
Keep the questions coming.