@OperationOne 

To get your network neat and clean with IPv6 you need a head IPv6 router that claims your  /56 from your ISP on the outer side (surely through DHCP6, see below).

Then on this IPv6 router on the inner side, the DHCP6 server shall be activated with DHCP6-PD option activated and tuned. PD is for prefix delegation.

I suggest you to start to delegate sub-network based on /64 slices. You'll be allowed to use 256 subnetworks. Routes declaration will then be fully automatic.

There's basically no need of static routes with IPv6 (especially if you've  got one of these d*mn*d ISPs who uses to change your IPv6 prefix randomly !).

Setting subnet with IPv6 works right out of the box and is a basic feature ; a feature which is fully plug-n-play. DHCP6 is mainly designed for routers.

Your ISP has a good documentation over this. I'm sorry but i just read the pfsense one which is detailed enough. I don't read italian but it is quite easy to follow.

The main question is : does your deco in router mode embeds DHCPv6 client tuned do perform prefix delegation acquisition as any IPv6 router do ? (IPv6 setup is quite obscure in the HMI).

Then SLAAC (RA server)  by a deco is really sufficient to push your IPv6 subnet and gateways  to your devices as automatically as it could be imagined.

The second main question is : is the SLAAC server that provides announcement of routers on your subnetwork activated on your master deco in router mode by TP-link and update itself according to the upstream PD ?

Note : a master deco could be an IPv6 head router is all this is activated. And if the deco can do PD for itself by reserving one subnetwork. (depending on TP-link implementation of IPv6 router mode within this master deco).

I didn't try that on my own network, i stayed with AP mode : prefix delegation is performed by my own router. I need a H24 IPv6 network : i can't break it for now. But anyway subneting with IPv6 is peaceful compared to the hell of IPv4 (far from NAT and static routes for example) : you just have to align your subnets routers behind the head router. in IPv6 and fire them all at once.

So as conclusion : give a try to prefix delegation in cascade to perform subneting using a master deco as subnet router behind your master one.

Regards,

Eric.