Hi. Will this Seagate Backup Plus Hub 10 TB External HDD attached on the usb 3.0 port work with this router as my network storage? For download and store movies on it?
Routers on USB aren't built to support it (Asus mentions max. 4TB), maybe it can work though, limits are not only HDD space but amount of files on other things too.
And it is not very reliable, use a NAS instead!
A proper NAS will give better performance and a more stable router/network too. (Even if it works somehow, as @Grisu points out above).
Let the router do the routing and find another/better solution for your storage sharing needs. Using the router to do this will be the worst of both worlds (ignore the marketing).