Most likely you probably have the older ONT that doesn't support the Gig so they will come out upgrade that and run ethernet. But just to be safe it doesn't hurt to mention it.
Sometimes people complain on here about using VPN with the G1100 but if you will be internet only you can use the Orbi or any other router and don't even use the G1100 at all. I'm just assuming the DD-WRT can also be the primary or you put that on LAN side or router. Either way you won't need to use the G1100.
I use a variety of streaming services with the G1100 and a Ubiquiti router and never had any issues is years.