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It depends how complex you want to get. At the most simple end, you can have a single router spitting out a single wifi network, and assigning IP addresses on a single range, e.g. 192.168.1.X. There are recommended IP ranges for certain devices, but that's mainly to aid compatability with other devices on the same system, e.g. an Ion, Gio, and Eos. If you've just got a single Ion, then any IP range will work. Make sure you give the devices you want to connect to a static IP.
TP-Link routers are generally good starting points. Their interface is usable and clear, and they're well-supported and very common. I'd advise one with dual-band wifi (2.4Ghz and 5Ghz) and putting it in a place where it has line-of-sight of the stage - that'll give you the best signal quality on-stage and in the auditorium, which is where I presume you'll be using it the most.
If you want to go more advanced with a more complex system, I personally use a UniFi system with two access points (one on-stage, another in the control box), and VLAN separation of the video and lighting control networks, with two separate wifi networks, but that's likely more advanced than you need.
Also, the ETC remote control app is a bit rubbish, so I'd highly reccommend the oscRFR app by Alien Stagecraft (iOS app, Android app). It requires setting up OSC on your console, but the website has instructions for it, and it basically gives you the whole button layout and customisable direct selects pages, it's great. Of course, you might only have basic needs, so the ETC RFR app might be good enough, though they do still charge for it I believe.