I work for a lubricant manufacturer in a sales/technical role and have done for 22yrs. I’ll offer my 2p worth from the oil side.
My database suggests you need a 5w30 or 5w40 oil meeting the VW specifications you mention. To simplify things you are most likely to find a 5w30. Don’t worry too much about that difference. The 5w30 part refers to the oils viscosity characteristics (it is an SAE 5 oil when cold (Winter – hence the w) and has polymers that make it behave like an SAE 30 when hot) and is not indicative of quality. The small numbers and letters refer to the quality and performance of the oil. There should be a generic API rating for petrol engines, currently at around SL/SM/SN And then brand specific ratings such as the VW 504.00 / 502.00. These indicate the quality and suitability of the oil.
Don’t worry too much about semi/fully synthetic, if it meets the VW spec it will be fine. I always refer to car oil semi/synthetics as Semi-semantics, its word play, it (well, a few exceptions, mostly found in motorsport oils) all comes from crude oil and refers to how refined it is, and what catagory of base stock is used to make the oil. No need for any more on that here…
Don’t get too hung up on the service interval/long life element of the specs especially if you are running ~10k miles per year. Both will be fine. I’m not too familiar with those specs but I’d expect that the difference is primarily in the additive package with a higher level of detergent/dispersant to clean the oil and possibly a higher level of high catagory base stock to resist degradation. Both oils will lap up sub 10k annual mileage with annual changes.
Oils will readily mix. The only oils that don’t mix are Poly Glycol Synthetics, and they typically go no where near a car engine. Some people have a vested interest in perpetuating myths about oils.
Petrol engines are more forgiving of poor oil selection than Diesel engines. DPFs are notorious for sensitivity to the wrong oil.
The point about petrol stations bring overpriced is a good one. Go to a trade motor factor, get an oil filter as well, and if you really want to protect your oil, a new air filter. This is often overlooked. I’d echo those warning against overfilling too.