yes, you can access the SPI at the pinheader at the top of the CONTROLLINO. So, you should not order the “PURE” variant
When you will be looking for a shield – choose the one which is 5 V compatible. When it is declared that it works (from performance point of view) with Arduino UNO, then it will work fine with CONTROLLINO MINI, when it is declared that it works fine with Arduino MEGA, then it will work fine with Arduino MAXI or MEGA.
Any plans to make a CAN (for my needs, J1939 compatible) compatible Controllino or at least a din-rail-mountable sidecar? The industrial form factor is appealing, but if I have to budge an arduino shield next to it, kinda ruins it. Thanks!