I thought the 2nd service was the same as the 1st but with pollen filter if needed and transmission check but I may be wrong...
I started doing my own services once my 2016
Ibiza Ecomotive was out of warranty. As I'm on a normal service regime (don't believe in long life) the service notification comes up annually as either "Oil Service" or "Inspection Service" which I tend to think of as a "small" or "big" service. Being now retired I'm typically doing around 6 to 8,000 miles annually. According to my Haynes manual 6451 the small service consists of an oil and filter change plus checking out the thickness of brake pads and resetting the service indicator. (typically I check out a lot more than this just for my peace of mind). The larger service includes the above with, as you say, a new pollen filter being fitted - by the way well done Seat, it's one of the easiest pollen filters to change that I've ever done! - However there is also a whole load of "stuff" (exhaust, hoses, oil leaks, aux belt, brake hydraulics for leaks, headlight beam setting, etc, etc, etc) which is visually checked. Probably the brake fluid should be changed at two years but I have a "proper" boiling point fluid checker so only change brake fluid when it no longer meets spec. Sounds and looks impressive on paper but probably takes an experienced Tech only minutes to do. Air filter and spark plugs get done at 4 years but I do the air filter at 2. The timing belt on mine (3 cylinder CHZB) is recommended for inspection at around 55,000 miles with further inspection at every additional 20,000 miles. In my experience timing belts generally either look absolutely fine or you're taking the covers off because it's gone Bang! so good luck with the 20,000 mile inspection interval. Mine will be renewed every 50,000 miles or 5 years whichever comes first. Interestingly perhaps? when I first serviced it, so it was four years old by then, although the front wheels came off relatively easily, I had the very devil of a job with the rears. The alloy had corroded to the hubs - I don't think the rear wheels had been off since she rolled out of the factory? All rubbed down and coated with anti seize now though!
I know I'm always interested in what brands other people are using so just for your interest I use Fuchs Titan GT1 Pro C-3 5w-30 engine oil - I've been using Fuchs in all the family cars for some years now with entirely satisfactory results - and I use either genuine filters or Mahle brand which I've used for over 20 years and never had a
problem. I'm a great believer in buying a good quality oil - that doesn't mean necessarily the most expensive - and doing regular oil changes. I would be most reluctant to go over 12 months or 10, maybe at a pinch, 12,000 miles. One of the family vehicles is used for business and does around 15.000 miles a year. It gets it's oil changed every 6 months, is now well over 100,000 miles and running very well. (although it did need new VVT pulleys at around the 100,000 mile mark). Transmission oils are very specialist now a days so I tend to only uase the actual oil specified by the manufacturer. Can be a little expensive but you don't need much of it. By the way I don't believe in "sealed for life" All the "Family fleet" get gearbox oil changed at 50,000 miles - or thereabouts and I believe this policy really pays off as I can't tell you when we last had a transmission failure. If you have an automatic I would say this is even more important, especially with the semi automatic/manual (ie DSG type) boxes which are popular today.
I'm a bit "precious" about all the cars I look after - there are 6 in the family - and I do pretty much all the service work myself only employing an "outsider" if it's something too heavy for my creaky old body to cope with. I've built up a wee network of specialist independent workshops who do things like clutches and heavy work for me. All staffed by main dealer trained techies who have set up for themselves so have "the knowledge" There's a wee 2 man Honda specialist, a medium sized Vauxhall specialist, AVW for my VAG stuff, you get the idea. The Fast Fit type operations can be very useful for stuff like wheel alignment, replacement tyres, and especially for weekend emergencies - our local Halfords have got me out of trouble more than once - but they wouldn't be getting their mitts on any of the technical parts of any of "my" vehicles.