Osram are about the best as other members have used them:
Also this link might help you choose too:
https://www.autoexpress.co.uk/accessories-tyres/41141/headlamp-bulbs-tested
Welcome to the forum you'll find the members on here are a friendly and helpful bunch 🙂 stunning looking A5 you have there.
Regarding upgrades you might find you can Psy for them on Audi connect. Heres info on it:
The sensors can pick up of there's something is blocking the roof movement. We've had other members who have had shoes and all sorts blocking the roof mechanism. Check behind the rear seats.
In failing that I'd advise a diagnostic check.
Petrol is definitely best for the driving you do. One main issue is the brake servo restricted issue. You'll find an extensive post about it on here. Also check out YouTube for some good buyers guides.
Yep you could get one made by a Russian company for various Audi models including the c5. Was contemplating one for when I can get back out on my more scenic road trips lol.
Looking online.it appears to be grey. Think the S3 had a green one?
This link might help too:
https://www.pelicanparts.com/techarticles/Audi_B6_A4/13-WATER-Coolant_Temperature_Sensor_Replacement/13-WATER-Coolant_Temperature_Sensor_Replacement.htm
We'll be getting to the show for 9ish. For the heads up there won't be a club display at this event. But we'll look forward to seeing any members who attend 🙂