It seems that there is no device support alternate gateway in DHCP reservation.

Whether all devices can not connect to AC3200 5G wifi. Or just one device can not connect to it. Maybe there is compatibility between your device with AC3200 5g.

Archer D20 support PPTP, L2TP, IPSec Passthrough. So if there is another router connected with Archer D20, the router connected with Archer D20 is able to dial-up PPTP, L2TP, IPSec VPN. And if you...

Do you mean you wanna replace the wireless router by TL-WR902AC? If that you can do the similar configuration at TL-WR902AC, but the fire stick need to connect to 902 via wireless, due to 902AC only...

Maybe we need contact the TP-LINK support. http://www.tp-link.com/us/support/contact-technical-support

I think the TP-LINK specifications shows function of the newest version. Such as v11 and v13, I can find the guest network. And you can check whether there is a new firmware for 841N_V9, maybe it can...