Request installation at rims/tire purchase 🙂

Hello together! I drive a Golf V and wanted to buy for this now new summer rims + tires. I was thinking about the Tzunamee of Barracuda in 9×19/9×20?. Am I not sure which size would be the right one now.(235/? R19 or 225/? R19) Unfortunately I don’t know about the Et either. Bzw. would it be better if smaller tyres are mounted on the front all back? I am grateful for any advice! 🙂 Lg