What format is the drive itself? If it's Mac HFS+ formatted it will not work. You'll need either FAT32 or EXT format. Macs will read either of those fine.
The 802.11ac range will be limited by environmental factors in your house like all wireless. You'll have to test how it performs at your place.
And if I get web6000q extender. Will I be able to use the same SSID for the 5ghz 802.11ac network? Or will it have two different SSIDS?
I really like how my apple time capsule/airport express setup works. Same SSID. And when I move around the house with my devices. They move to the better Access point seamlessly.