I you can afford one, the iPad Pro will handle the mostest and need the least external accessories.
11" 128GB WiFi only being the cheapest model.
The earphone socket audio quality on a pro is very good, good enough not to have to do external analog to digital conversion out the USB C port, so no need for a Korg Plugkey. The headphone output can go straight to the mixer with a 1/8" TRS to twin 1/4" TS cable. Plus the USB C port can be plugged into AC power all the time, essential onstage.
https://kenrockwell.com/apple/ipad-pro-audio-quality.htm
I recommend grounding the iPads AC charger using the Apple 3 pin plug with the earth being a true metal pin not a plastic one (or none at all). This is to avoid a ground loop, creating a buzzing in your audio feed to the mixer. The Apple grounded 3 pin plug slides onto the iPad AC charge transformer in place of the one which came with the iPad.
The wifi on the iPad is actually a very useful way of getting the band song tempo into the iPad, using Ableton Link which is built into many iOS apps, you don't need Ableton to use link, you just need other computers or devices with Link on using the same wifi network. Include a wifi router near the stage and everyone with a link enabled computer or device logs onto that private wifi and then sync instrument tempo automatically using Ableton Link.