[Help] Ryzen 7 9700X (€200) vs Ryzen 7 7800X3D (€244) - which one to buy for online gaming (DayZ / Dota 2) + possible streaming?

Hi everyone, I need some advice choosing a CPU. I can get the following deals with AliExpress coupons:

• AMD Ryzen 7 9700X - €200
• AMD Ryzen 7 7800X3D - €244

My setup / use case:

• GPU: 9070 XT
• RAM: DDR5 6000 CL30
• I mostly play online games, especially DayZ and Dota 2
• I don’t work on my PC, but I might want to stream in the future
• Planning to buy a second 1440p (2K) monitor

Questions:

1. Which CPU makes more sense for my use case, especially for online / CPU-heavy games?
2. Is the extra €44 for the 7800X3D worth it over the 9700X?
3. What kind of CPU cooling would you recommend (air vs AIO)?
4. Is the MSI MAG B850M Mortar WiFi the best value motherboard, or are there good cheaper alternatives worth considering?

Thanks in advance for any advice 🙏