No you don't and yes, APX is quite common for engine swaps with less "accessory" 

I started off with an APX and like you found very limited mappacks for it.
The conversion to ME7.5 is really not that difficult, in essence just a few new wires for a wideband sensor and cutting one of the fan controller pins.
As a noob, I found wideband tuning to be a lot more forgiving as the ECU does not go open loop on WOT.
There is a BAM ols floating around that can then be used as a starting point.
The rest of the stuff can be mapped out via the software (VVT, EGT, rear o2, rear cat)