Existing Fortigate dual wan setup, trying to introduce SDWAN

We have an existing Fortigate 7.4.11 firewall configuration with 100+ firewall policies and 10 VPN, IPSec connections and 2 WAN connections. 

We are wanting to now configure SDWAN to handle the 2 WAN Connections. Has anyone retrospectively added SDWAN to your existing config? 

We are looking for options.

Current options seem like

1. configure SDWAN and remove all references to the WAN interfaces (ie assigning those references to some other interface), then building SDWAN and reassigning to the zones. 

 Pros: point and click

 Cons: take the network down for a bit while this configuration is being done and then troubleshoot issues

2. dump the config, and integrate the changes, then try to import that new config into the fortigate

 Pros: seems quick, little downtime

 cons: seems like it will fail. 

3. script the changes and dump those into the CLE

 Pros: seems quick, prone to errors

 cons: troubleshooting after it fails

4. Building another SDWAN zone with a 3rd wan connection

 Pros: move policies one at a time, test along the way

 cons: not sure Fortigate will allow this

Any recommendations?

Thanks