Mode 22 is "request diagnostic data by PID" -- a diagnostic service provided by the ECU. Mode 01 is generally what's called the "SAE generic" PIDs for basic stuff like rpm, coolant temp, etc. Mode 22 PIDs are manufacter/ECU specific, but can give you more of the data that you really want/need for tuning-- knock, boost above 22psi, etc.
Most of the top commercial solutions offer something even more advanced which is an ECU patch to enable high speed direct RAM logging. Mode 22 is nice, but we only have what VW/Continental decided to give us. There's a few nice to have things missing...but most of what you need is there.
MPI split is not available via mode 22 logging, but you can log DI and MPI injector pw separately.
As far as the box code thing.....yes, you can pretty readily find most stock tune files online to flash with the software. No issues changing box codes, you can flash to whatever you want...you just want to know what you're doing a bit. For example if you flashed a GTI file onto a R, it would immo brick. But cross flashing a common or consolidated box code/ROM is pretty common for these cars.