Do I need a fume extractor, or is a window fan enough?

If you can duct outside, duct outside — a 4-inch inline fan pushing through a window board beats most desktop filters and never needs replacement cartridges. A recirculating extractor is for when outside venting is impossible: it must be sized to your machine and its carbon stage is a consumable you will replace.

The failure mode to avoid is the middle path: a filter too small for the machine, saturating quietly while the room absorbs what it misses. Budget extractors by airflow (CFM) against your enclosure volume, not by the marketing photo.