How much RAM/CPU — common question.
By traffic
500-2K — 1GB. 2K-10K — 2GB. 10K-50K — 4GB. 50K+ — 8GB.
By CMS
Static — 512MB. WordPress — 1-2GB. WooCommerce — 2-4GB.
Database
MySQL — 2-8GB cache. Big sites — separate server.
SSD vs NVMe
500MB/s vs 3GB/s.