Those are outputs, and no, it just means that there are 6 cables coming out of the PSU that are suitable for high power pci-e load. If the description on the EVGA site is correct then the configuration of the cables is 2x 750mm, 900mm (m) 4x 750mm (m). So you've got 2 cables with 2 connectors each, and 4 cables with one connector each — 8 pci-e connectors in total. What I don't like about EVGA is that they often over-complicate things with pci-e connectors (probably because this particular PSU is an old design back from 2013). With this PSU not all eight connectors are 8-pin, only six of them are and then the remaining two are 6-pin. That is not likely to be a problem in your case (unless you've got some rare 970s — which ones do you have anyway?).

In terms of wattage, 1000W is fine for your rig. You'd get a little bit higher efficiency if you'd use a 1200-1300W PSU, but considering how you're using older-gen cards it looks like power efficiency is not exactly your main priority. So 1000W will be enough.