No, he means forget about having speakers in the rear altogether. They will only hurt soundstage and imaging, they're detrimental to the overall response not helpful in any way. With the front stage done right you'll never miss those rear speakers, ever. You can take the budget you were going to spend on rear speakers and put it toward the installation on the front stage.
As for which model of miniDSP you need, I probably wouldn't suggest tackling a 3 way setup for your first time going active. There's a great deal to learn about how to tune just a 2 way (tweeter, woofer) setup let alone to add another driver (tweeter, midrange, woofer) to the mix. A 2x4 miniDSP should be all you need to start with. Later on down the road another 2x4 can be added when you're ready to tackle a 3 way. There's not enough going on in the subwoofer realm to NEED to run its signal through the DSP.