FMAB is 64 episodes. A high-quality 1080p pack should be roughly 30GB to 60GB . If a "complete series" is only 5GB, the visual compression will be severe (heavy pixelation).
When using torrent downloads, it's essential to consider the following: Fullmetal Alchemist - Brotherhood Download Torrent
Availability varies by country, but it frequently carries the series. ⚖️ A Quick Note on Ethics FMAB is 64 episodes