Nighthawk X4 AC2200 Wifi Setup

Hey guys, hoping to learn how to install these range extenders so that I can advise clients to by them to fix their Range issues.

I will be setting up an Nighthawk X4 AC2200.  It will be all wireless with the  Access Point/Extender switch Turned On.  We will be using a Comcast Xfinity Modem Router. 

1. My question is (as it is not clear in the instructions on the Netgear PDF Online) Can I, or should I, use a Ethernet Cable to setup Wifi?  I did this once before using the All Wifi Method, following all the instructions online (To make sure they were the most current).  It was not very successful, though eventually it worked AFTER I left the Clients house!  Really weird and not good.  This is why I am hear, trying to clear up these issues.  So what is the BEST way of doing this? 

2. Also, it appears that I can Turn On the Access Point/Extender Switch right away, and not wait till Step Five on the List?

Hope this thing works out or we won't buy any more of these devices.

Thanks, NetworkMaster