Hi rob1nzon,
Advanced -> Advanced Network ->Traffic management -> Bandwidth profiles
- Add a profile
  - Name: MYLIMIT
  - Policy type: outbound
  - Profile type: Rate
  - Set minimum and maximum bandwidth rate with the values you want.
  - Choose your WAN interface
  - Save settings
Advanced -> Advanced Network ->Traffic management -> Traffic selectors
- Add
   - Available profiles: MYLIMIT
   - Service: choose the service you want to the limit applied to, for example HTTP
   - Traffic selector MAtch Type: BSSID
   - BSSID: Choose here the BSSID of your WiFi network
   - Save settings
To apply this limit to all services, you can create a custom service in Firewall Settings -> Custom services (for example a custom service called ALL_SERVICES with type "Both" (TCP and UDP) and a Port Range between 1 and 65535).
Let us know if it works.
Cheers.