The release notes for Moodle 3.5 (the latest version) are here - https://docs.moodle.org/dev/Moodle_3.5_release_notes. This tells you what Moodle's requirements are. 200 users isn't a lot but it depends what they are doing (all 200 logging in at the same time to do a quiz is a different thing from logging in occasionally to browse resources)
Given a free choice I would use Linux rather than Windows. You'll certainly get more help here. Windows expertise is a bit thin on the ground.