Openreach modem to BT Home Hub 4

Sky fibre unlimited will be installed next week. So I will be getting an Openreach modem and Sky hub. AIUI the Sky hub (router) does not have 5GHz and I would like to add that.

As it so happens I have an opportunity to acquire a BT Home Hub 4 at a discount. This has concurrent 2.4 & 5.0 GHz. I am wondering if I could use that instead? Or can I add the Home Hub 4 as an access point?

What would happen if I connected the HH4 to the Lan 2 port on the modem?

Thanks,

Best to add the HH4 as an access point, just turn off it's DHCP and connect it LAN-LAN. I don't think LAN2 on the modem will give you internet access, you have to connect to the Sky hub.