This is a good article which will probably answer a lot of your questions: https://www.autosport.com/f1/news/2025-british-grand-prix-how-to-get-silverstone-tickets-and-when-do-they-go-on-sale/10634195/
As for the 24 hour priority, I would say no but I haven't bought a ticket for the last 2 years and haven't experienced the new purchasing system, so I can't say for certain. If you know exactly where you want to sit and are going to be buying multiple tickets in an expensive grandstand, it might be worth it. Unfortunately, Silverstone employ the scummy "dynamic pricing" model, so don't be surprised to see tickets prices increase in front of your eyes.