Apple iPad Air Wi-Fi + 4G LTE (First Generation)

Will this iPad work on just wifi? Where do I get a SIM card? Can. Take one out of an older iPad mini?

Yes, it will work on Wi-Fi just fine. You would get the SIM card from your data carrier.

I don’t really care about the 4G LTE. Can I just choose not to activate that and only use the Wi-Fi, or do I have to set this up through my wireless carrier? I really don’t want to add another device to my plan.

For just Wi-Fi, no need to contact a carrier. Just connect to your Wi-Fi network as usual.