FortiGate 50E - Maximum WAN Links Permitted

I know that the FortiGate has a WAN1 and a WAN2 ports. Can a 50E use a total of 3 or 4 WAN connections assigning 1 or 2 of the Internal ports to serve as additional WAN ports? Can this be done using either fail-over or SD-WAN? In this application the options are limited to multiple relatively slow connections from the ISP.