This is slightly complicated by the VAG approach to servicing based on age or mileage. New cars often come pre-set with Longlife servicing requirements, where the on-board computer senses the need for a service at any time up to 18,600 miles or 2 years maximum.
My understanding is that Longlife is intended for cars that tend to do longer journeys and dictates the need for a more thorough "inspection" service when the car asks for one. This is at 2 years for many people.
However, diligent dealers will set a car's OBC for annual servicing if your car usage is mainly around town, infrequent journeys etc. In this latter case, you will alternate between a less thorough "oil change" at the first year and then the inspection at the second anniversary.
Oil change services for A3s tend to be at or slightly lower than £200, then around £375 for the inspection service. This is comparable or cheaper than other brands, certainly cheaper than Volvo in my experience.
Obviously many people interpret the above in their own way and may just go with the cheaper Longlife / 2-year servicing schedule while still theoretically maintaining a full history.
Like you, OP, I have ordered a new A3 which I hope to keep for many years alongside another older VW product - neither of which will do big mileages but will continue to be annually serviced. You can of course choose to do servicing outside the official network and still maintain the manufacturer warranty.