How much RAM do I need for Xcode and Docker on a MacBook Air?

Regarding the MacBook Air: Get 16GB. 8GB will hurt you daily because Xcode alone — the compiler, simulator, and indexing engine — is a memory hog, and adding Docker containers pushes you over 8GB before even opening Safari. macOS will then swap to the SSD, slowing everything down and wearing the drive faster. With 16GB you keep working; with 8GB you wait for apps to relaunch and the beach ball to stop. Your time is worth more than the upgrade cost.