I do this and it works really well. The quality and variety of synth and other musical apps available is absolutely incredible, even if you aren’t an Apple fan you won’t regret it. Trying to make full tracks on the iPad itself is still a bit painful but as a sound module its perfectly suited - checkout this thread iPad Music Apps? which points to many of the best apps.
I personally use the Apple Lightning to USB adapter (the one which also has a Lightning port, so you can charge the iPad at the same time) to connect my Focusrite 18i8 interface and it works perfectly for audio and MIDI. You can also use the Digitakt to drive the iPad via USB MIDI. I’ve got the iPad Pro 10.5" and its probably as powerful as most Macbooks, latency is not an issue at all.
My only advice would be to buy a fairly recent model as the power of iPads is increasing all the time, although you can get pretty far even with an older model. Also I’d ensure you have a reasonable amount of storage space (64GB minimum I think) as its easy to fill it up with apps and there is no way to increase the space after the fact!