I use Raspberry Pi 4 with 16GB SD-card. I simply don’t have enough memory and CPU power for 15 separate database containers for every service which I want to use.
Protondb - info about current state and playability of almost any game on Steam driven by community.
AFAIK many calendar apps use CalDAV protocol which is quite universal. So basically any compatible with CavDAV protocol app (Thunderbird, Evolution) will work just fine.
VS Code + some extensions - yes, I know that it is not an IDE. I use it for game development on Unity (C#) and it makes job done.
No.