You don't need to have two networks. You can connect the TP-Link to your ISP router as LAN-to-LAN. Then everything will be on the same LAN segment and you won't have any problems with file sharing, printers, etc....(i.e. you won't have a double NAT).
http://www.tp-link.com/en/faq-417.html
https://awesometoast.com/archer-c9/