SG-5100 with 3 WANs and 3 VLANs?
Is it possible to setup SG-5100 to use 3 ports for 3 distinct ISPs on load balancing Multi WAN, and the remaining 3 ports for 3 different VLANs with different firewall and proxy settings?
It has 6 independent ports so you should be fine. Each interface has its own firewall rules (or there can be floating rules).
For multi-WAN see https://docs.netgate.com/pfsense/en/latest/multiwan/index.html