Synology NAS W/ dual NIC ports to OPNsense lagg0 config

[jws37]

I have a BCM Advanced Research MX170QD mini itx board running OPNsense.
It has 2 nic's built in, i211-at (igb0) and i219-lm (em0)
I installed a dual port QNAP 2.5Gb nic, set it up as the wan & lan ports. (igc1-wan, igc0-lan)
The igc1 is connected to a Arris S33 modem.
The other port is connected to a 1Gb unmanaged switch.
This setup is working ok.

My next step is to get a 8 port 2.5Gb switch.
I want to connect the 2 (igb0, em0) network ports to my Synology DS720+ NAS.
This would eliminate the need for a smart switch to do the LAG setup.
It seems like all of the set up information I have found uses a smart switch to do the lag settings.

At this time I do not want to create any vlan's etc, if possible, and keep the setup as simple as possible.
The nas will not be accessed from the internet.

I got the 2 ports set up as lagg0: fast timeout, Hash layer-L3, Use strict-no, interface OPT1 created.
I set up the port 'bonding' on the nas and it used the existing gateway info.

I gather I need to create firewall rules, for OPT1, like the 'default allow' on the Lan port?
Then assign a IP address to OPT1 and set the nas gateway to that address?

I'm concerned that if I create a new subnet '192.168.2.x for OPT1
And the nas gateway to the same, if it does not work I will loose contact with the nas and need to reset it.

I got this far and I'm got over the last 'hurdle' to finish the setup.

Thanks for reading through this wall-o-text.