I think the problem here that most won't realize is that they'll have no idea what you're listening to and so will be mixing audio in the dark, so to speak. Professionals will check headphone mixes, but generally won't mix with headphones certainly not bluetooth headphones. I suppose there may exist such a thing as powered Bluetooth monitors, but again, the wireless Bluetooth, and what it does to audio, is the weak part in the chain. iPad built in speakers are not flat, so if you mix for them, the audio might only sound alright coming out of an iPad.
There are probably audio docks for iPad which will include a DAC for converting stereo sound from the iPad USB-C port, and jacks for monitors, but I have never seen one that doesn't have the cheapest components available. Not sure of the current abilities of iPad and USB-C, but last I heard, iPad was only capable of stereo in and stereo out. There's a lot that can be done with just two tracks, but do not doubt that everything depends on the converters and preamps, so a professional quality USB-C ADC/DAC with decent pres (unless off-boarded) is paramount to creating half decent tracks, which is paramount to creating very good mixes.
Not everyone is a professional audio engineer, and everyone here that is an expert at everything will likely be satisfied with terrible converters and the audio they produce. YMMV