@DJAA I think you might be mistaken since OSC does NOT work over MIDI. It requires a network connection.
@Syme It’s good you’re trying to achieve the simplest possible solution. So let me suggest you try the following:
- Use a direct connection between iPad and Mac with a lightning cable (no camera or ethernet adapters needed) and
- Use the OSC function of TouchOSC Mk1 instead of translating MIDI to OSC in a third-party app
The communication via direct USB connection works like this (the steps need to be done only once):
- iPad to Mac: Find out your Mac’s host name (like this) and use it for the “Host” field in TouchOSC.
- Mac to iPad: The iPad is automatically assigned an IP address when it is connected. It cannot be set manually. To find it out you need to use the command “arp -a” in the terminal or a free iPad app like Net Analyzer, for example.
Use this IP address for the “Remote Client IP address” field in Gig Performer.
(Please note that a fresh IP address is assigned if the iPad is restarted. In this case you need to repeat this step. Using standby or flight mode for the iPad does not require this.)
This trick was inspired by this great thread that even takes it a level further (too much for my personal requirements).
This is the simplest possible solution for the hardware-part I can think of. Let’s see if it works for you. 
The programming part is covered pretty well in the manual and in this forum, too, I believe.